In “Hiroshima in Iran: What Americans Really Think about Using Nuclear Weapons and Killing Noncombatants,” a pathbreaking survey of attitudes toward the laws of war published in the summer 2017 issue of International Security, Scott Sagan and Benjamin Valentino found that Americans are relatively insensitive to the targeting of civilian populations and to international norms and taboos against the use of nuclear weapons. We replicated a key question of this study, where respondents were asked if they would support saturation bombing an Iranian city to end a war. We also introduced some variations into the experiment to directly measure any potential influence of international norms and laws. Overall, our quantitative and qualitative findings are more optimistic than those of Sagan and Valentino's study: Americans do strongly believe it is wrong to target civilians. And in a real-life scenario such as this, a majority would likely oppose such a bombing. These findings suggest, however, that much depends on how survey questions are structured in measuring those preferences and whether legal or ethical considerations are part of any national conversation about war policy.


Do Americans believe in the laws of war, and would they follow them when it really counts? A landmark 2015 survey of public opinion on U.S. attitudes toward the laws of war suggested that Americans are relatively insensitive to even the most basic wartime taboos against the targeting of civilian populations and the use of nuclear weapons. In the survey, Scott Sagan and Benjamin Valentino asked a sample of Americans if they would prefer a U.S. strike on a city in Iran that killed 100,000 civilians if it would end a war and save 20,000 U.S. troops' lives. A majority of the respondents said that they would prefer such a strike, even if a nuclear weapon were used; and slightly more than two-thirds preferred the strike if it were carried out with conventional munitions. Sagan and Valentino concluded that “the majority of the U.S. public has not internalized either a belief in the nuclear taboo or a strong noncombatant immunity norm.”1

This conclusion, if true, is disturbing. Even in Sagan and Valentino's “less extreme” conventional saturation-bombing scenario, survey participants were invited to contemplate—and many preferred to go along with—a horrific war crime. Saturation bombing of undefended cities during World War II killed, by one scholarly estimate, perhaps 750,000 civilians—about seven times as many as died in the atomic bombings of Hiroshima and Nagasaki.2 Such massacres by air were singularly horrifying: a survivor of the Tokyo firebombing, who lived only because she was buried under bodies of her neighbors as they burned alive, described mothers fleeing the inferno while the babies on their backs caught fire. Many in Europe suffocated in cellars or were eviscerated by shrapnel in explosions. For good reason, saturation bombing, like other forms of civilian targeting, has been delegitimized as a method of war.3

Sagan and Valentino's inference that these norms are weaker than once thought is also disturbing—particularly their conclusion about the civilian immunity norm.4 Whereas the legality and morality of nuclear weapons use continues to be contested, it is widely believed that the prohibition on willfully targeting civilians in armed conflict is one of the oldest and most foundational norms of war.5 It is also now a legalized global prohibition norm, codified in treaty law since 1977 and considered part of customary law by the International Committee of the Red Cross.6 Thus, Sagan and Valentino's conclusion is a challenge not only for experimental studies of the civilian immunity norm specifically, which have tended to show that Americans strongly believe in it,7 but also for theories of norm effects and legalization in international relations.8

In this article, we revisit the strength and impact of the civilian immunity norm on American attitudes toward saturation bombing using Sagan and Valentino's Iranian scenario. A second look is warranted because the design of their experiment makes it difficult to know whether or not their finding is driven by the weakness of legal or ethical norms, by a lack of knowledge of or agreement with those norms, or by other factors such as framing effects—including Sagan and Valentino's choice not to mention international law or norms in their survey vignette, what we term “priming by omission.”

We replicated a key question in their study, where respondents were asked whether they would prefer launching the strike against the Iranian city or continuing the ground war against Iran. We also introduced some variations into the survey that allow us to tease out the strength and influence of norms relative to other factors. First, we created independent measures for knowledge of, agreement with, and sensitivity to relevant ethical and legal norms. Second, we created alternative versions of the question to test whether framing effects in Sagan and Valentino's experiment had driven their results.

Across a variety of measures, we found that international ethical and legal norms against civilian targeting do exert a significant constraining effect on U.S. public opinion. Accurate knowledge of international law matters, as does agreement that it is wrong to target civilians—a belief that we found to be held widely and strongly by Americans. Even being asked to think about international ethical norms prior to answering the question significantly decreased support for a strike.

We also found significant framing effects at work in Sagan and Valentino's experiment. In particular, requiring respondents to choose between dichotomous policy options exaggerates apparent support for unethical decisions and under-measures the effect of international norms on citizen preferences. A close examination of open-ended explanations of respondent answers provides a much more reliable (and more heartening) indicator of American attitudes. Indeed, many participants who “preferred the strike” in our survey were actually registering moral confusion, not a disregard for the lives of foreign civilians. Moreover, by asking other respondents to address the same dilemma in an open-ended manner, rather than requiring them to choose between two morally unacceptable options, we found even more clear and widespread opposition to the saturation bombing of civilians and significant respect among Americans for the civilian immunity norm, with a large majority opposing a strike.

Our conclusion is that even in this fairly unrealistic “hard case,” there is evidence of the “stopping power” of international norms. Moreover, the methods used to capture public opinion and the presence or absence of legal or ethical concerns can significantly amplify or mask that power. Therefore, the implications of this article go well beyond a reappraisal of U.S. attitudes toward the use of force, demonstrating the power and politics of public opinion polls and survey experiments in foreign policy.

In the remainder of this article, we first summarize Sagan and Valentino's landmark study and note some of the assumptions built into it. We next outline our research design: a set of survey experiments embedded at the start of a YouGov omnibus survey in summer 2018.9 We then describe our findings regarding the impact of international norms on U.S. attitudes toward saturation bombing. We conclude with some wider implications for scholars using survey experiments and suggestions for further study on norm effects in international security.

Revisiting “Revisiting Hiroshima in Iran”

Recent scholarship has explored the impact of U.S. public opinion on support for adherence to the laws of war,10 with public opinion, especially in democracies, expected to exert a constraining effect on state use of political violence.11 Many studies find a significant effect of international law on public attitudes.12 Sarah Kreps and Geoffrey Wallace's research on drones suggests that U.S. citizens are more persuaded by arguments that invoke international legal principles than military efficacy against terrorists.13 James Walsh argues that the promise of sanitized warfare that accompanies drones and precision weapons may result in a higher aversion to civilian casualties abroad.14 Wallace's findings on support for torture suggest that international law will affect public opinion even more in cases where external pressures to engage in the policy are at their highest.15

Other experimental studies cast doubt on these findings, concluding instead that there is no relationship between international law and public attitudes,16 or that Americans are more likely to use a “logic of consequences” when weighing foreign policy options.17 Some findings are ambiguous: Brian Rathbun and Rachel Stein's study of public sensitivity to nuclear first use shows that logics of consequences and appropriateness are not mutually exclusive—even consequences-sensitive survey respondents may in fact be expressing moral judgment, aiming to maximize the greater good by supporting a controversial security policy.18

These findings connect to a larger literature on norms and war. Some scholars argue that an array of humanitarian norms have rendered war both less frequent and less bloody,19 including norms against the use of weapons of mass destruction (WMD), assassination, and strategic bombing.20 These norms have become embedded in military organizations in ways that incentivize limits on the use of force and benefit civilians.21

Yet, some scholars of international norms are more skeptical about the stopping power of either law or public opinion on state behavior in war.22 Their research finds that democracies target civilians to avoid incurring casualties and domestic pressure to end wars of attrition.23 Such states comply with the laws of war only when they expect reciprocity.24 States pressured to adhere to international law develop strategies and adopt creative interpretations to avoid being bound by it.25

It should be noted that these studies look at what states do, not at what their publics want. Two trends in the wider literature, however, provide purchase on the idea that public attitudes can influence the strength and impact of international norms. First, it is often assumed that states, or at least democracies, will be responsive to public pressure in foreign policy matters.26 Second, while international norms operate politically primarily at the elite level where foreign policy decisions get made, significant adoption of a norm by the public can serve as an indicator of the strength of international norms in wider political culture.27

In the context of this theoretical debate, Sagan and Valentino sought to test whether the nuclear taboo and the civilian immunity norm would exert a significant taming effect on American public attitudes should the United States face a Hiroshima-like dilemma.28 In an era where a sitting U.S. president has blithely referred to both nuclear weapons and the targeting of civilians, this question is hardly academic, and it is no surprise that their study was widely read.29 It was the most downloaded article from MIT Press in the year it was published, and received significant attention from U.S. policymakers and the media.30

In Sagan and Valentino's experiment, 780 Americans read a version of a vignette stating that the president was considering (variously) either a nuclear or conventional weapons strike on a foreign city to “end a war” that would otherwise kill an additional 20,000 U.S. ground troops. The respondents were then asked to signal how much they preferred to “continue [the] ground war” or “launch [the] strike,” and also whether they would “approve” of the strike or not regardless of their preference. About two-thirds preferred striking the city with conventional weapons, killing a projected 100,000 civilians. Sagan and Valentino inferred that the U.S. public has not internalized the civilian immunity norm.

Although we do not dispute Sagan and Valentino's overall finding, we argue that it requires further study for three reasons. First, even if one takes their empirics at face value, their inference is surprising. The scenario they created was truly a hard case for restraint, with every possible interest-based reason to target civilians baked into the vignette. One should not expect 100 percent norm adherence under such conditions. Indeed, in the absence of robust ethical norms against nuclear use and civilian targeting, one would expect unanimous support for the strike. Even so, Sagan and Valentino found significant percentages of Americans opposing such strikes—affirming previous scholarship demonstrating that norms always interact with interests.31 Rather than expecting Americans to eschew civilian targeting under these conditions and decrying those who do not, we should be heartened that a considerable number are willing to do so even in the anonymous format of a survey designed in ways that incentivize norm violation.

Second, and more importantly, inferences about the robustness of a norm and its effects on policy are not possible without independent measures of the norms themselves.32 Sagan and Valentino's experiment diverged from other recent experimental studies in that it did not include a treatment involving norms and taboos.33 Moreover, the authors gathered no data on attitudes toward or fluency in the norms themselves on the part of the respondent sample.34 Norms are “counterfactually valid”35—for example, the willingness of some people to drive drunk (or go along with their friends who do) does not invalidate the strong norm against drunk driving. So the strength of norms cannot be determined simply from analyzing individual behavior.

Third, in Sagan and Valentino's experiment, underlying U.S. awareness of and sensitivity to important international norms cannot be disentangled from the effects of introducing intervening variables known to increase public willingness to violate international norms. Americans weigh their concern for foreign civilians against their concern for force protection, military casualties, or threat perception.36 Because norm conflicts can reduce support for prohibition norms in warfare, pitting the protection of Iranian civilians against the protection of U.S. troops could have biased Sagan and Valentino's experiment in favor of striking the city.37

Moreover, the putative cause of the war—an Iranian nuclear weapons program—may lower the threshold for advocating any kind of attack for two reasons. First, there is a clear analogy here to the main justification for the 2003 Iraq War: Iraq's supposed possession of WMD. The power and flexibility of the idea of WMD, combined with the exhortations of the George W. Bush administration, provided a powerful rationale for a preventive attack and set a significant precedent as the first war fought to counter weapons of mass destruction.38 As of 2015, 42 percent of the U.S. public still believed that the United States had found weapons of mass destruction in Iraq.39 The power of analogies for foreign policy is well known and may easily have influenced respondents.40

Second, the perception that Iran might use nuclear weapons offensively against civilians of another state could contribute further to justification for a massive preventive strike. Some analysts argue that a nuclear-armed Iran would give Iran an incentive to strike first, increase the risk of nuclear war against Israel and the United States, or possibly both.41 Support for a military strike on Iran even in the absence of a war was already high (at 37 percent) in 2018.42 Indeed, among voters who believe that Iran will very likely develop nuclear weapons, 53 percent think that it will use them to attack the United States.43

Moreover, the violation of a norm is likeliest when the motivation to do so is very high and a respondent is not constrained by the need for social approval.44 The structure of a survey experiment in which respondents are told that U.S. soldiers' (and maybe civilians') lives are on the line (high motivation to violate), and are free from social opprobrium for their choice (given that surveys are anonymous), seems very likely to yield a higher number of pro-civilian-targeting responses than would be likely in ordinary conversational settings. Although this may accurately mirror the ways in which the media might attempt to measure public opinion in an actual political crisis, it does not necessarily follow that these are the best measures of the underlying norms.

Numerous scholars have also noted that embedding disputed assumptions in survey experiments as “facts” may bias respondent answers.45 We note such contested assumptions in Sagan and Valentino's experiment, in which the initial vignette presents an air strike as a viable option for ending the war in a situation that is clearly analogous to the nuclear strikes on Japan. Whether the atomic bomb ended World War II, however, is the subject of dispute.46 There is even less data to support the claim that saturation bombing cities or other forms of civilian targeting end wars.47 Next, there were only two options given, one of which was to “continue” the war rather than end it, leading respondents to believe that other options are unavailable in such a situation.48 Moreover, while these disputed assumptions are embedded in the story and the survey question, undisputed factual information about relevant U.S. treaty obligations is conspicuously absent.

Sagan and Valentino's finding is interesting and provocative in and of itself. But given the array of other factors that could yield their finding, it is unclear how much this finding says about the strength of the immunity norm or the nuclear taboo. In short, given the lack of discussion or testing of legal or ethical norms and a Hiroshima-like force protection scenario involving weapons of mass destruction that allows only two choices, this is the type of fictional experiment and question structure that we might least expect to showcase the stopping power of the civilian immunity norm. Consequently, it is difficult to gauge the strength of the norm and its impact, or to separate its impact from framing effects without further study.

Research Design

To explore what the Sagan and Valentino experiment says about U.S. attitudes toward the civilian immunity norm, we conducted a follow-up survey experiment to test a number of hypotheses. We embedded Sagan and Valentino's news article and question (henceforth the Iran scenario question) as the first item in a YouGov omnibus survey:

Given the facts described in the article, if you had to choose between launching the strike against the Iranian city or continuing the ground war against Iran, which option would you prefer?49

Respondents were asked to indicate the strength of their preference between these two options on a scale from 1 (“strongly prefer to continue ground war”) to 6 (“strongly prefer to launch strike”). We chose the version of the question where respondents were asked about what they would “prefer” rather than what they would “approve” precisely because we are measuring norm effects, and as Sagan and Valentino note, this is the best indicator of respondents' “beliefs about what is ethical and appropriate military behavior,” without priming them about what policymakers might or might not do.50 Our survey went out to 2,500 participants, with 250 participants receiving this replication version of Sagan and Valentino's article and question.

To test a number of framing effects, we provided the remainder of the participants with variations on the article, the question, or both. We aimed to test the effect of knowledge of international legal norms as well as respondent sensitivity to the specific norm of civilian immunity.51 We tested for three different norm effects on respondents' policy preferences. First, we tested respondents' knowledge of the law on civilian immunity with a simple true/false question, which is a better test of the effects of law than simply providing information because many respondents may already know the law.52 In our survey, respondents were asked: “As far as you know, which statement is more correct? (1) Under international law, it is sometimes permissible to directly and intentionally attack the civilian population in war; or (2) Under international law, it is never permissible to intentionally and directly attack the civilian population in war.”

Second, we tested respondents' sensitivity to the immunity norm. Respondents were asked how strongly they agreed or disagreed on a scale from 1 (strongly agree) to 5 (strongly disagree) with the statement “It is wrong to intentionally and directly attack the civilian population in war.” We also asked respondents to explain their answer, allowing them to outline conditions under which they thought it might be ethically permissible to target civilians. We were thus able to take a direct measure of Americans' sensitivity to the immunity norm independent from testing the effect of the norm on their policy preferences.53

Third, we examined whether simply priming respondents to think about ethical norms made a difference in their answers. Agreeing with the immunity norm is different than being primed to think about it. A person who strongly agrees with ethical norms may still disregard them if not primed to consider them, and a person who does not agree might still feel the weight of them if primed.

Our base hypothesis (H1) was that our results would replicate Sagan and Valentino's finding that about two-thirds of Americans would choose to kill foreign civilians rather than accept losses of American soldiers. We varied the ordering of the above questions in ways that allowed us to test our hypotheses that support for a strike would decrease with prior knowledge of the legal norm (H2); with agreement with the underlying ethical norm (H3); and after priming about that ethical norm (H4). Because some participants received these questions before they were asked whether to bomb the Iranian city, and some after, we were able to test, rather than simply guess at, these effects.

Finally, although we adopted Sagan and Valentino's fictional scenario as a hard case for civilian immunity, we wanted to know whether their result could be related to another framing effect given the closed structure of the Iran scenario question itself, which included a number of contested assumptions baked into the narrative and forced respondents to choose between two undesirable outcomes. Despite being a good measure of how Americans might respond to a dilemma posed in this way, their finding might not accurately portray policy discussion in a real-world situation or be a good indicator of U.S. moral reasoning

Consequently, we hypothesized (H5) that an open-ended query might also decrease strike support. In our version of the survey, an additional group received an open-ended (instead of a closed-ended) version of the question: “Given the facts described in the article, if you were the Commander in Chief of the United States military, what would you do and why?” Such an approach—measuring how Americans grapple with an ethical dilemma in their own words—provides not only a measure of how framing effects may have mattered here, but also a clearer measure of the impact of the immunity norm.

What Do Americans Really Think About Noncombatant Immunity?

Overall, our quantitative and qualitative findings are less pessimistic than Sagan and Valentino's. Worded exactly as they designed the experiment, it is not surprising that our initial replication largely confirmed their survey result: under certain conditions, a majority of Americans surveyed would support saturation bombing an Iranian city, given the facts as expressed in the vignette and with no changes in the structure of the question.54 It is notable, however, that whereas Sagan and Valentino found that 67 percent of respondents supported a strike, we found that only 57 percent did so—an interesting shift since Donald Trump became president.55

What we cannot know from Sagan and Valentino's original research design is whether the majority in favor of the strike is a result of the weakness of the immunity norm or of its strength being offset by other factors, including the framing effects embedded in the experiment. To determine the strength and impact of the immunity norm, we conducted a number of other tests. We tested variations of Sagan and Valentino's original research design against a slightly modified version of our initial replication in order to control for the factors that caused the decrease in support from 2015 to 2018.56


First, we examined the extent to which Americans indeed understand U.S. obligations under international law (H2) or agreed with the ethical content of the immunity norm (H3). If international legal or ethical norms (or priming about those norms) make a difference in respondents' preferences, we would expect to see answers to the scenario question differ depending on their answers to the legal and ethical norm questions, and on whether or not they considered these questions before or after answering the Iran scenario question.

Here, our findings are far less pessimistic than Sagan and Valentino's. When respondents were asked about international law before the Iran scenario question, a significant number (80 percent) were able to accurately state that targeting civilians is a war crime absolutely prohibited by international law (H2). Respondents' level of accurate international law knowledge also affected their preferences: 72 percent of those who answered the law question incorrectly supported a strike, whereas only 45 percent of those who answered correctly did.57

Second (H3), we found strong evidence of agreement with the civilian immunity norm among the U.S. public. About 80 percent across all groups who were asked the question somewhat or strongly agreed with the statement that it is “always wrong” to target civilians: only about 10 percent disagreed, and 10 percent were “not sure” when asked prior to the Iran scenario question.58

In addition to asking our respondents whether they agreed that it is always wrong to target civilians in war, we allowed them to explain their answers. In particular, we invited respondents who did not agree with the statement to elaborate on the conditions under which they would consider targeting civilians, before introducing any information about the law or a fictional news article. This included the 10 percent of people who were “not sure.” We found that the moral views of Americans are far more nuanced than they may be able to express on a single closed-ended Iran scenario question that forces them to choose between terrible options.

When asked to explain their answers, those who “strongly agreed” with the prohibition on civilian targeting as an absolute rule cited the principle of “defenselessness” or “nonparticipation” undergirding humanitarian law, as well as more abstract normative principles such as civilian “innocence” or the “Golden Rule,” or they stated that it was “just wrong,” with a few mentioning that targeting civilians could also be counterproductive.59

What is most notable, however, is that many of these respondents balked at providing any explanation at all when asked to explain their answer, with variations of the following: “You just don't do that,” or “Because it's wrong to kill civilians,” or “Why would you even ask such a thing?” Several respondents wrote answers along the lines of “I shouldn't have to explain why this is murder.” Many wrote variants of “WTF?” when asked to consider this question.60 This “taken-for-grantedness” of the civilian immunity norm by many respondents indicates the robustness of the norm in the minds of Americans.

Although an open-ended question about civilian immunity might gauge the strength of the immunity norm, it might not be a good measure of the norm's influence on public opinion in a given policy scenario. It is one thing to believe in the ethical validity of a norm; it is another for that norm to impact preferences when actors are highly motivated to violate a norm, as they would be when asked to trade foreign civilian lives against the lives of U.S. troops.61 To measure the impact, we examined whether agreement with the norm in principle correlated to preferences for the strike. Given that a substantial majority (61 percent) across all groups strongly agreed that it was wrong, we compared the “strongly agree” group with all other groups. To minimize any priming effect, we measured approval only in the groups that were asked for their preference for a strike before asking whether they agreed with the ethical norm. Only 39 percent of those in the “strongly agree” group supported a strike in this scenario, versus 74 percent of those who did not strongly agree.62

Just thinking about the immunity norm prior to expressing a preference made a difference in expressed preferences. Respondents who were primed (H4) by being asked about agreement with ethical norms underlying international law prior to being asked about the Iran scenario—regardless of their answer to the norm question—were less likely to prefer the strike (46 percent) than those who were not (54 percent).63

Together, these findings lend credence to previous studies that show that Americans are sensitive to the civilian immunity norm, and that the majority are willing to insist that the United States should not intentionally harm civilians even in foreign policy crises.64 That this effect holds up even in such a hard case as the dilemma presented by Sagan and Valentino confirms the stopping power of international law and norms.


If Americans agree that targeting civilians is wrong, why did a majority of them nonetheless appear to prefer to bomb a city? In particular, what explains the group of respondents who say they agree that bombing civilians is wrong but support it anyhow? To explore this question, we looked closely at a particular subset of respondents—those least likely to want to bomb the city, but who leaned toward the strike anyway—and examined the explanations they gave for their preferences on the Iran scenario question to try to better understand what might sway such individuals to nonetheless express a preference for a war crime. This population of 104 open-ended comments consists of all respondents from each of two treatment groups where there was no priming in advance of the Iran question, who first chose either 4, 5, or 6 on the question about the Iran scenario and then chose “strongly agree” on the query about agreement with the ethical norm.

We want to emphasize that this group includes those who leaned at all toward the strike, whether weakly (4), moderately (5), or strongly (6). The explanations that the weak-strike supporters gave demonstrate that they do not actually prefer the strike. Rather, they are ambivalent or confused. From analyzing their explanations, we conclude that two factors unrelated to the strength or weakness of the immunity norm may be driving that result: embedded assumptions/analogies and the closed-ended nature of the survey.65

contested causal assumptions and historical analogies. Our first observation is that some respondents appeared to discount the horror of saturation bombing in their answers, indicating that they did not intend to support civilian targeting and that they expected civilians would have the chance to flee. For example, one wrote: “If our military is not gaining ground quickly, then yes, air strikes will need to happen. I know most citizens of that country are told before air strikes. So those people can move away from the area.” Indeed, many respondents in this group appear to be voting not in favor of targeting civilians and more against continuing what was portrayed in the vignette as a costly, ineffective, and bloody ground war. Twenty-one percent of comments received an “End the War” code capturing this sentiment, and 9 percent were coded “Lessen the Bloodshed,” where participants believed that a terrible crime now could end the war and prevent future deaths on both sides, civilian and combatant.

We see this response as a reaction to two highly contested assumptions built into both the vignette and the structure of the question—that a saturation bombing strike against a city of civilians would definitely end the war, and that the only other option was to continue a ground war. Respondents were told in the headline of the vignette that the air strike was being considered “to end [the] war,” and the phrasing of the question asked them to choose between “launch strike” and “continue ground war.” Comments indicate that respondents interpreted the strike on the city as a guaranteed means to end the war and bring the troops home, so respondents who preferred not to continue the war may have leaned toward the “strike” end of the scale despite their antipathy to targeting civilians, because there were simply no other good options given. For example, some comments read:

I would wish this war never started, but to end the loss of lives, warning needs to be given to move Iranian people to safe places with short notice and then begin the strikes to stop the bloodshed and the armaments. It needs to stop.

I would not want to go to war in the first place but if we had and if airstrikes would ultimately save life's [sic] and end the war quicker then I guess that would be best!

Weighing the risks, Iran would be much more likely to surrender after an air strike, whereas a ground war would only continue to rack up both American and Iranian casualties.

Why continue with a ground war when an airstrike would possibly end the war? I would give the civilians of a particular city 24 hours to evacuate before I bomb it.

These respondents—like many others in this subgroup and elsewhere in our larger dataset—appeared to subscribe to a kind of “dirty hands” ethics: the belief that in certain situations a terrible crime might be justified to achieve an equally important goal—in this case, not simply protecting American lives (which mattered greatly to 36 percent of our respondents) but also ending a war that might, they thought, otherwise kill more people on both sides. When we systematically coded responses, more respondents in this group exhibited an “end the war” mentality (21 percent) than either an “anything to win” mentality (14 percent) or a “bomb them all” mentality (4 percent); 14 percent of them stated they wanted to protect civilians nonetheless. Thus, we observed that for this group, a retributive-justice attitude mattered less than a willingness to accept at face value the erroneous claim embedded in the vignette that the strike against a civilian city would end the war—a war that they believed would put not only U.S. troops, but also foreign civilians, at ongoing risk.

This entire line of ethical thinking hinges on respondents' acceptance not of a moral principle but of an utterly fallacious causal claim: that a single saturation strike would end the war. Leaving aside that there is no known case in history of a saturation strike against civilians having that effect, what matters is that respondents accepted the stated assumption in the fictional story that it would have such an effect. It is difficult to imagine the same individuals agreeing to strike the city if they correctly understood that the war would almost certainly continue and perhaps escalate.

We thus think that a second factor contributed to respondents' willingness to both set aside their strong moral aversion to killing civilians as such and suspend their disbelief that a strike could end the war: the Hiroshima analogy embedded in the structure of the story itself. Although historians dispute whether the atomic bombings actually ended the war, and although there is no evidence that firebombing was effective at forcing German or Japanese surrender, various open-ended comments in this subgroup indicated that they believed it was the strategic bombing of civilians that ended World War II (WWII) as a justification for their answer:

We had the same decisions to make in WWII. They are horrifying but necessary.

This fictional situation obviously mirrors the dilemma of how to end the Second World War, with attacks on Japanese populations through both firebombing and the atomic bomb. It showcases the difficulty in trying to make moral judgements in a time of war. There is the possibility of viewing attacks on civilians as a moral action, in that they could tend to end a war more quickly, and thus reduce overall casualties, despite the immediate ugliness of the action.

Just as with the dropping of nuclear bombs on Japan in 1945 based on projected American casualty figures. The bombing of targets that will force the enemy to end hostilities is preferable.

Consistent with this “historical analogy” hypothesis, of those respondents who both strongly agreed with the immunity norm but also strongly preferred to strike the city in the Iran scenario, several indeed invoked World War II analogies in their explanations, indicating both agreement with the immunity norm and a belief that because an attack would “end the war,” it would be the lesser of two evils:

This is the same problem that the US had when they dropped the nuclear bomb on Japan and the war was over.

This is a similar situation that we found ourselves in WWII against Japan…. The USA made the correct decision in WWII which is what we should do in this situation.

If the World War II analogy is driving respondents to support the strike, Sagan and Valentino's study (and our replication) may show less an indifference to the immunity norm than the power of historical analogies (even misleading ones) in public opinion polls, and a willingness to accept embedded causal assumptions given to respondents by an authority figure such as a pollster (such as the idea that saturation bombing can end wars), for the purpose of answering a hypothetical question. We doubt whether such findings would be externally valid in a real-world version of this scenario for reasons we elaborate in the conclusion.

the tyranny of closed-ended questions. We also think that a framing effect was created through the either/or structure of the Iran scenario question in both Sagan and Valentino's survey and most of our replications. Because many, if not most, respondents exhibited mixed feelings, and therefore were distributed somewhat at random into categories 3–4, collapsing the categories 4–6 into a single code for “prefer strike” overestimates actual strike support. The ambiguity of what “3” meant compared to “4” was not lost on respondents: several who selected “4” on the survey explained their answers this way:

I picked the middle button because I really don't know. I hate to think American soldiers are dying in the ground war, but it is also not right to kill a bunch of civilians.

The question posed was a false dichotomy. My preference would be to withdraw as the nuclear and other military targets had already been removed. There is nothing more to gain.

I don't think this is an either/or situation. With the ability to pinpoint munitions, a concerted effort to destroy Iran's infrastructure should be the next military objective. A propaganda campaign should also be launched to persuade the general population to denounce their leaders' actions.

I answered “4” because this article is not realistic. The scenario described doesn't reflect US military strategy and capabilities.

Well firstly, I wasn't given a whole lot of choice, as I would have chosen the option “don't know.”

Holding other framing effects constant, we wondered how much strike support would shift if respondents were permitted to consider the same scenario without being boxed into expressing an either/or preference. To examine how much of the explanatory work is being done by this type of framing effect, we adopted Sagan and Valentino's fictional scenario but changed the structure of the question (H5). We allowed one group of respondents to read the same vignette as the rest, but instead of providing them with the same closed-ended answer forcing them to choose between only two options, we asked them to think in an open-ended manner about what they would do in this scenario if they were the commander in chief. These respondents still understood that the assumption in the scenario was that the attack would end the war—the title of the vignette was “President Considering Major Air Attack on Iranian City to End War”—and that they were being asked to choose between two different options. What was different was that respondents were not required by the structure of the question prompt either to choose between those options, or to uncritically accept the assumptions in the article that these were in fact the only two options.

A group of 234 respondents answered this question. To arrive at a result that we could compare to our closed-ended answers, we conducted a second rigorous qualitative analysis of all their open-ended answers aimed specifically at determining which respondents “chose” either of the two options versus how many thought outside the box. Of these, we found a remarkable drop (relative to the “choose between two undesirable outcomes” closed-ended version of the question) in the proportion of those who would support saturation bombing civilians. Whereas 57 percent of Americans in our original replication leaned toward striking the city when forced to choose between two options, this percentage dropped to 34 percent on the open-ended answers.66 But neither did most Americans choose instead to continue a costly ground war—only 51 percent of respondents were satisfied with either of these two options, with 42 percent suggesting a range of alternative options. As with the comments from the fence-sitters in the closed-ended version of the question, many of the most popular suggestions included negotiating a conditional surrender, conducting an air campaign only against military targets, withdrawing to end the war, or seeking the help of allies to negotiate a peace.67 A small percentage (6 percent) also criticized the question itself:

This scenario is utterly unrealistic…. Please.

Wonder why I was given news about an imaginary war. Therefore, the question makes no sense.

Where did this article come from and what is the reliability of it? I would want more credible facts/information regarding this article before I would make an important decision of killing civilians.

Our open-ended data from this group also offers a more hopeful picture than Sagan and Valentino about the narratives that Americans employed. As in the earlier analysis, we specifically looked for a pattern in our open-ended answers that Sagan and Valentino flagged in theirs—an atrocity-minded attitude toward foreign civilians among those who saw them as guilty and worthy of retribution.68 We called this code “bomb them all” and did indeed find a few examples of this co-occurring with “strike city” sentiment—but only among 6 percent of overall respondents.

By contrast, we also looked for answers that explicitly invoked the civilian immunity norm, a code we called “don't target civilians.” Three times as many respondents (17 percent) specifically mentioned the norm against targeting civilians as exhibited a “bomb them all” mentality. For example:

I would call the Joint Chiefs together and tell them what has been presented is unacceptable in terms of lives lost on the parts of both the United States and Iran, and that other options need to be developed … including the possibility of ending the conflict using diplomatic means.

I would not authorize air strikes against civilians. The nuclear capability and air response has been negated. It would be an unnecessary slaughter of civilians, Iranian military persons and American lives for no purpose other than being a vengeful bully. Diplomatic efforts would be required.

If I'm stuck with the facts above, I would reject the part of the “shock strategy” that targets Mashhad and kills 200,000+ civilians. That kind of strategy only would rally the Iranian people and harden opposition. Clear goals need to be set at the outset…. The goal of replacing the government is unrealistic folly—with whom? There's also a huge risk of Russia entering into the conflict and it widening to include Israel—a wider regional war with greater risk of use of tactical nuclear weapons. Seek a truce; freeze in place. “Statements” about unconditional surrender can always be walked back from. Dead troops and civilians can't be brought back to life.

In short, although we do not doubt that some of those who argue for targeting civilians would justify their positions using such dehumanizing rhetoric, we do not find such respondents representative of the wide swath of U.S. public opinion. Rather, they are outliers, outnumbered greatly by those who would invoke the immunity norm to justify opposing such action—or, at least, restraining it.

Thus, we find the either/or question posed by Sagan and Valentino to their respondents, like most closed-ended surveys, cannot accurately measure the nuance and complexity of U.S. public opinion and may have driven some respondents to register an inaccurate preference. This particular dilemma as expressed, and especially combined with an either/or prompt, obscured the general antipathy of Americans to using saturation bombing to solve foreign policy problems. For these reasons, as we discuss further below, we suspect that Sagan and Valentino's initial finding offers only a limited guide to how Americans might react to such a situation should it occur in the real world.


Our findings suggest that the decline of U.S. support for the civilian immunity norm has been somewhat exaggerated. Yet, when it comes to the norm's impact on political attitudes, Sagan and Valentino's finding and ours jointly suggest that it matters greatly whether and how those norms and laws are disseminated to and activated among the wider public. Because international norms are contextual and contingent, they have a stronger effect when invoked as a form of communicative action.69 A political debate—or a fictional survey experiment—in which the laws and norms are never mentioned as a relevant consideration is likely to blunt their impact, thus increasing measured support for illegal acts, unethical acts, or both.

Based on our analysis, we suspect that Sagan and Valentino's result was driven less by overall U.S. indifference to the laws of war than by the way that the design of the experiment primed respondents to disregard moral and legal taboos by focusing in detail on tactical cost/benefit ratios expressed through contested causal assumptions and emotionally charged historical analogies.70 Simply put, the presence of “tactical” primes (U.S. soldiers' lives were at stake; the war would end if civilians were killed; and other options were unavailable, just like Hiroshima) coupled with the absence of “normative” information (e.g., the United States has signed treaties prohibiting the targeting of civilians even under these circumstances) may have biased Sagan and Valentino's experiment in favor of a logic of consequences rather than a logic of appropriateness.71

Ironically, Sagan and Valentino specifically chose not to integrate any mention of U.S. legal obligations into the experiment in a well-intentioned effort to avoid bias:

We have been careful in these experiments not to “prime” the respondents in ways that might bias the results. For example, in our stories, we did not mention the possible environmental effects of nuclear weapons. We described the victims as “civilians” rather than “innocent women and children.” We mentioned only “immediate deaths and long-term fatalities” from the nuclear attack, and did not describe the gruesome details of fatal burns or radiation sickness. We did not raise the possibility that an attack targeted against a city as a “shock strategy” would violate both the laws of armed conflict and U.S. nuclear weapons employment guidance, and thus would also likely be opposed by many senior U.S. military leaders.72

Choosing to refer to civilians accurately as civilians rather than inaccurately as “women and children” is certainly a careful, sound choice.73 The existence of a rule against targeting civilians is not only a “possibility,” however; it is a highly relevant social fact based in customary treaty law and U.S. military doctrine.74 The absence of discussion of this rule along with other relevant information allows for a misunderstanding by respondents of the acceptability of the scenario among the international community and U.S. military. The exclusion of these facts thus produces a priming-by-omission effect because the facts that matter in preference formation are likely to be the ones with which respondents are presented.75

Also, we know from the literature on norms that norms are salient precisely when they are brought to mind in the context of a policy decision. Furthermore, the literatures on norm revisionism and norm decline suggest that a strategy for minimizing the strength of a norm is to remove it from political discussion.76 Respondents may have believed that they were specifically being asked to disregard moral or legal considerations by the way in which the question was asked. There is some support for this hypothesis in Sagan and Valentino's open-ended comments in their own survey. As one respondent wrote:

Prefer this option I did not. I marked it in the middle only because I was given no option “Neither.” If you ask what option I would propose—it would be Bomb the Palace in Teheran, not in some other city! Bomb the infrastructure to disrupt the supply lines to the Iranian troops on the front lines. Thus, the casualties (on both sides) would be minimized (at least to some extent), and efficiency of the US actions would be increased.

Regardless, what no doubt weighed heavily on all respondents' minds were the tactical primes: information about casualties, war aims, and war prospects. Sagan and Valentino explain their emphasis on tactical primes by arguing for the need to re-create the Hiroshima dilemma faced by policymakers at the end of World War II. Their reasoning is that scenarios featuring a Hiroshima-like “trade-off are arguably among the most realistic and serious conditions in which a president and the public would be forced to contemplate the use of nuclear weapons in the future.”77 Much to their credit, they adopted troop casualty numbers that reflect some of the best estimates of the number of deaths that would have occurred in a ground invasion of Japan rather than the “half a million lives saved” myth.78 Consequently, the vignette and question do lead to the same kind of scenario that U.S. policymakers faced when electing to attack a city in World War II rather than, for example, conducting a demonstration strike.

Something crucial to the validity of the experiment has changed since Hiroshima, however: the normative context. The saturation and nuclear bombings of cities during World War II led to the rise of powerful and widely held normative prohibitions against strategic bombing of civilians.79 As one of our survey respondents put it in an open-ended comment:

Iran is not Japan—there are codified international laws that must be abided by if we're to continue to call ourselves a nation governed by the rule of law. Purposefully targeting civilians for a strike of any scale, let alone this large, would be an egregious violation of the Geneva Convention. Dresden, Hiroshima, Nagasaki … these should be viewed as lessons on what not to do, not blueprints to reuse.

Indeed, the civilian immunity norm, once a loose set of ethical rules, has been codified into treaty law and is so widely incorporated into military manuals that it is now considered a part of customary international law.80 Opprobrium against nuclear weapons has reached the point that a multilateral treaty has been negotiated—if not yet entered into force—banning their use entirely.81 Although scholars disagree on whether these norms would likely constrain the use of force in certain scenarios, what is certain from our analysis and many others' is that U.S. political and military elites and ordinary citizens have internalized these norms.

Consequently, any public debate on bombing civilians today, whether with conventional or nuclear weapons, would certainly include invocations of those laws and norms by an array of actors including some political elites, many nongovernmental organizations, a number of important international organizations, and likely the Joint Chiefs of Staff themselves.82 It is thus unlikely that a vignette that includes tactical information but not accurate portrayals of legal or normative arguments correctly captures the situation the U.S. public would face in a potential Hiroshima-like scenario in today's world.

A number of recent studies in international law and public opinion emphasize how such framing effects of surveys can either capture or dampen measured U.S. sensitivity to international norms, predisposing respondents toward policy positions they might in fact abhor. For example, a systematic discursive analysis of nearly 200 U.S. national security poll questions determined that the structure of the questions in many cases predisposes respondents to disregard international law and ethics in favor of tactical concerns or misinforms respondents about the nature of U.S. treaty obligations.83

Another study examined poll questions whose findings show widespread U.S. support for drone attacks and determined that they typically “presented as uncontroversial two main assumptions about the U.S. drone policy … first, that the policy adheres to IHL [international humanitarian law] and second, that it has legal authorization.”84 By conducting a survey experiment where some groups were given more or less accurate information about U.S. legal obligations, the study found public support for drone strikes to in fact be much more heavily contingent on perceived adherence to the immunity norm than suggested by mainstream polls.

In light of these findings, we argue that what Sagan and Valentino have demonstrated is not the weakness of the immunity norm or the nuclear taboo, but rather the ability, by framing a dilemma in purely utilitarian terms and invoking historical analogies, to increase public support for attacking civilians despite the stopping power of international norms.85 We are thus less convinced by the inference that Americans are generally insensitive to international rules and norms on civilian immunity—though that sensitivity does vary and also seems related in part to whether or not international law is invoked in the context of a political discussion.

If anything, our measures of international law sensitivity are conservative, because we asked respondents only to think about the norms themselves, in isolation from any social context other than the survey experiment; in real life, they would be subject to many social pressures. A vignette could include information on what political elites, generals, human rights groups, or other U.S. citizens were saying, creating intersubjective as well as subjective context to mirror what Americans might feel in the real world.86 Future studies might explore these alternative vignettes.


Our augmented replication of Sagan and Valentino's study on civilian immunity suggests that while their finding that a majority of Americans would prefer a strike against the city of an adversary under the conditions specified was accurate, their conclusion about the weakness of the immunity norm was premature. Instead, we find that a majority of Americans believe strongly in this norm, and that it affects political behavior when Americans believe in the norm, know it is enshrined in law, or even are asked to think about it before expressing a preference. This norm has an effect even in survey scenarios where the deck is psychologically stacked in favor of atrocity.

Our experiment confirms a second policy-relevant argument about how international norms work: that the stopping power of ethical and legal norms is enacted through a dynamic of communicative action in which actors make choices about how and whether to invoke norms.87 In conversational settings where considerations at play carefully exclude the role of law and ethics, their impact will be weaker than in settings where participants are provided information or primed to consider them.88 Predictions that scholars can make about public support for saturation or nuclear bombing in a future war scenario hinge greatly, therefore, on the extent to which norms, laws, and ethics would be a part of any such political conversation.

What will matter in preventing the use of saturation bombing or nuclear weapons against Iran or North Korea will not be the nascent goodwill of the American people, but the ability of international law–minded actors to influence the parameters of political debate. Indeed, a key effect of international treaty law is empowering domestic publics and activist elites to weigh in on political debates.89 Recent survey experiments suggest that Americans are highly likely to trust sources such as human rights organizations and modify their opinions based on their recommendations.90

An additional consideration raised by the combination of our study with Sagan and Valentino's is the power of survey experiments themselves to shape public opinion. Some public opinion pollsters regularly field surveys designed to predispose public debate toward the narratives of political elites rather than international law–minded actors.91 Thus, we take seriously Sagan and Valentino's question about whether U.S. public opinion would encourage or discourage a president to use nuclear weapons in international crises. We argue the answer is that it depends on how that public opinion is measured.

Therefore, we wish to conclude by raising an important “so what?” question begged by all these studies on public attitudes toward the laws of war. It is important to note that nothing in the laws of war states that adherence or obligation to treaties is or should be dependent on the whim of the national public. Rather, the laws of war bind national-level policymakers and soldiers. It is not anticipated by most war law advocates that the general public is informed or cognizant of the nuanced distinctions in international ethical rules. Rather, it is very much anticipated that the public is fickle and security minded in time of war. Therefore, this and other studies on U.S. attitudes toward the means and methods of combat must be taken in context.

Several factors beyond our own survey result give us cause for optimism. Senior members of the military pushed back when Republican presidential candidates spoke of carpet-bombing Iraqi civilians.92 A new global humanitarian disarmament treaty has been negotiated by middle-power states and global civil society organizations banning any use of nuclear weapons, potentially increasing a stigmatizing effect.93 Additionally, the robust civil society response to U.S. violations of the laws of war mitigated and rolled back those violations after the George W. Bush presidency.94

In sum, studies consistently show that the U.S. public is generally in favor of the United States following its international legal obligations—whatever those may be. International treaties are designed to protect both enemy and American civilians from the scourge of war. It is therefore important to make efforts to minimize public fickleness or confusion at the meaning of the law. National leaders and military personnel must be held to their legal obligations to bolster the stopping power of norms.


The authors are grateful to Scott Sagan and Benjamin Valentino for inspiring this project, sharing their data for replication, and providing feedback on early drafts; to Samantha Luks at YouGov for assistance with survey design and Victoria Duran for assistance with coding; and to the participants at the International Studies Association workshop on Expanding the Nuclear Taboo and panel on Experimental Methods in Foreign Policy, at the University of Massachusetts Amherst's Conflict, Violence and Security Workshop and at Stanford University's Center for International Security and Cooperation, Political Science Department, and Workshop on Nuclear Weapons and International Law for feedback on earlier versions of this article. They are especially thankful for feedback from Janina Dill, James Fearon, Peter Haas, Colin Kahl, Meredith Loken, Rose McDermott, Joseph Nye, Brian Rathbun, Kenneth Schultz, Geoffrey Wallace, and Allen Weiner.



Scott D. Sagan and Benjamin A. Valentino, “Revisiting Hiroshima in Iran: What Americans Really Think about Using Nuclear Weapons and Killing Noncombatants,” International Security, Vol. 42, No. 1 (Summer 2017), p. 60, doi.org/10.1162/ISEC_a_00284.


See data from Alexander B. Downes, Targeting Civilians in War (Ithaca, N.Y.: Cornell University Press, 2008). See also Alexander B. Downes, “Civilian Deaths from Strategic Bombing in the World War II Era,” unpublished memorandum to Charli Carpenter, 2019. The immediate deaths from Hiroshima and Nagasaki totaled 100,000–115,000. See The United States Strategic Bombing Survey: The Effects of Atomic Bombs on Hiroshima and Nagasaki (Washington, D.C.: U.S. Government Printing Office, June 1946). For other estimates, see Richard Overy, The Bombing War: Europe, 1939–1945 (London: Penguin, 2013).


Ward Thomas, The Ethics of Destruction: Norms and Force in International Relations (Ithaca, N.Y.: Cornell University Press, 2001); Tami Davis Biddle, “Strategic Bombardment: Expectation, Theory, and Practice in the Early Twentieth Century,” in Matthew Evangelista and Henry Shue, eds., The American Way of Bombing: Changing Ethical and Legal Norms, from Flying Fortresses to Drones (Ithaca, N.Y.: Cornell University Press, 2014), pp. 27–46; and Giovanni Mantilla, “Social Pressure and the Making of Wartime Civilian Protection Rules,” European Journal of International Relations, Vol. 26, No. 2 (June 2020), pp. 443–468, doi.org/10.1177/1354066119870237.


While Sagan and Valentino refer to “noncombatant immunity,” this term encompasses not only the civilian immunity norm but also the prohibition on willful killing of wounded or captured noncombatant soldiers (those hors de combat). Instead, we use the term “civilian immunity” to refer more restrictively to the normative principle that the civilian population specifically shall not be the object of attack.


See Fen Osler Hampson, Madness in the Multitude: Human Security and World Disorder (Don Mills, Canada: Oxford University Press, 2002); and Colm McKeogh, Innocent Civilians: The Morality of Killing in War (Basingstoke, U.K.: Palgrave Macmillan, 2002). Although powerful, this assumption is erroneous. See Simon Chesterman, ed., Civilians in War (Boulder, Colo.: Lynne Rienner, 2001); R. Charli Carpenter, “Innocent Women and Children”: Gender, Norms, and the Protection of Civilians (Aldershot, U.K.: Ashgate, 2006); and Helen M. Kinsella, The Image before the Weapon: A Critical History of the Distinction between Combatant and Civilian (Ithaca, N.Y.: Cornell University Press, 2011).


Article 51 of the 1977 Additional Protocol to the Geneva Conventions states, “The civilian population as such, as well as individual civilians, shall not be the object of attack. Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited.” See also Françoise Bouchet-Saulnier, The Practical Guide to Humanitarian Law (Lanham, Md.: Rowman & Littlefield, 2002), 1st English-language edition, ed. and trans. by Laura Brav. The International Committee of the Red Cross (ICRC) considers this “Rule 1” among those rules considered to be customary law. See “Rule 1: The Principle of Distinction between Civilians and Combatants” (Geneva: ICRC Customary International Humanitarian Law Database, 2005), https://ihl-databases.icrc.org/customary-ihl/eng/docs/v1_rul_rule1.


See, for example, Adam S. Chilton, “The Laws of War and Public Opinion: An Experimental Study,” Journal of Institutional and Theoretical Economics, Vol. 171, No. 1 (March 2015), pp. 181–201, doi.org/10.1628/093245615X14188909230370; James Igoe Walsh, “Precision Weapons, Civilian Casualties, and Support for the Use of Force,” Political Psychology, Vol. 36, No. 5 (October 2015), pp. 507–523, doi.org/10.1111/pops.12175; and Sarah Kreps, “Flying under the Radar: A Study of Public Attitudes towards Unmanned Aerial Vehicles,” Research & Politics, Vol. 1, No. 1 (May 2014), pp. 1–7, doi.org/10.1177%2F2053168014536533.


Ethan A. Nadelmann, “Global Prohibition Regimes: The Evolution of Norms in International Society,” International Organization, Vol. 44, No. 4 (Autumn 1990), pp. 479–526, doi.org/10.1017/S0020818300035384; Wayne Sandholtz and Kendall Stiles, International Norms and Cycles of Change (Oxford: Oxford University Press, 2009); Kenneth W. Abbott et al., “The Concept of Legalization,” International Organization, Vol. 54, No. 3 (Summer 2000), pp. 401–419, doi.org/10.1162/002081800551271; and Matthew Evangelista and Nina Tannenwald, eds., Do the Geneva Conventions Matter? (New York: Oxford University Press, 2017).


Charli Carpenter, “Strikes on Civilians” (Redwood City, Calif.: YouGov, July 15–19, 2018).


Daryl G. Press, Scott D. Sagan, and Benjamin A. Valentino, “Atomic Aversion: Experimental Evidence on Taboos, Traditions, and the Non-Use of Nuclear Weapons,” American Political Science Review, Vol. 107, No. 1 (February 2013), pp. 188–206, doi.org/10.1017/S0003055412000597; Chilton, “The Laws of War and Public Opinion”; Geoffrey P.R. Wallace, “International Law and Public Attitudes toward Torture: An Experimental Study,” International Organization, Vol. 67, No. 1 (January 2013), pp. 105–140, doi.org/10.1017/S0020818312000343; Kreps, “Flying under the Radar”; and Walsh, “Precision Weapons, Civilian Casualties, and Support for the Use of Force.”


Ole R. Holsti, Public Opinion and American Foreign Policy, rev. ed. (Ann Arbor: University of Michigan Press, 2009); Beth A. Simmons, Mobilizing for Human Rights: International Law in Domestic Politics (Cambridge: Cambridge University Press, 2009); Richard C. Eichenberg, “Victory Has Many Friends: U.S. Public Opinion and the Use of Military Force, 1981–2005,” International Security, Vol. 30, No. 1 (Summer 2005), pp. 140–177, doi.org/10.1162/0162288054894616; and Joseph M. Grieco et al., “Let's Get a Second Opinion: International Institutions and American Public Support for War,” International Studies Quarterly, Vol. 55, No. 2 (June 2011), pp. 563–583, doi.org/10.1111/j.1468-2478.2011.00660.x.


Michael Tomz, “Reputation and the Effect of International Law on Preferences and Beliefs,” working paper, Stanford University, 2008.


Sarah E. Kreps and Geoffrey P.R. Wallace, “International Law, Military Effectiveness, and Public Support for Drone Strikes,” Journal of Peace Research, Vol. 53, No. 6 (November 2016), pp. 830–844, doi.org/10.1177%2F0022343316657405.


Walsh, “Precision Weapons, Civilian Casualties, and Support for the Use of Force,” p. 519.


Wallace, “International Law and Public Attitudes toward Torture.”


Adam S. Chilton and Mila Versteeg, “International Law, Constitutional Law, and Public Support for Torture,” Research & Politics, Vol. 3, No. 1 (January–March 2016), pp. 1–9, doi.org/10.1177%2F2053168016636413.


Scott Sigmund Gartner, “The Multiple Effects of Casualties on Public Support for War: An Experimental Approach,” American Political Science Review, Vol. 102, No. 1 (February 2008), pp. 95–106, doi.org/10.1017/S0003055408080027; Grieco et al., “Let's Get a Second Opinion”; Michael C. Horowitz, “Public Opinion and the Politics of the Killer Robots Debate,” Research & Politics, Vol. 3, No. 1 (January–March 2016), pp. 1–8, doi.org/10.1177%2F2053168015627183; and Courtenay R. Conrad et al., “Threat Perception and Public Support of Government Torture,” working paper, University of California, Merced, 2015.


Brian C. Rathbun and Rachel Stein, “Greater Goods: Morality and Attitudes toward the Use of Nuclear Weapons,” Journal of Conflict Resolution, Vol. 64, No. 5 (May 2020), pp. 787–816, doi.org/10.1177/0022002719879994.


On frequency, see Oona A. Hathaway and Scott J. Shapiro, The Internationalists: How a Radical Plan to Outlaw War Remade the World (New York: Simon & Schuster, 2017).


Thomas, The Ethics of Destruction; Richard M. Price, The Chemical Weapons Taboo (Ithaca, N.Y.: Cornell University Press, 1997); and Nina Tannenwald, The Nuclear Taboo: The United States and the Non-Use of Nuclear Weapons since 1945 (Cambridge: Cambridge University Press, 2007).


Theo Farrell, The Norms of War: Cultural Beliefs and Modern Conflict (Boulder, Colo.: Lynne Rienner, 2005); Jeffrey W. Legro, “Which Norms Matter? Revisiting the ‘Failure’ of Internationalism,” International Organization, Vol. 51, No. 1 (Winter 1997), pp. 31–63, doi.org/10.1162/002081897550294; and Colin H. Kahl, “In the Crossfire or the Crosshairs? Norms, Civilian Casualties, and U.S. Conduct in Iraq,” International Security, Vol. 32, No. 1 (Summer 2007), pp. 7–46, doi.org/10.1162/isec.2007.32.1.7.


Benjamin Valentino, Paul Huth, and Sarah Croco, “Covenants without the Sword: International Law and the Protection of Civilians in Times of War,” World Politics, Vol. 58, No. 3 (April 2006), pp. 339–377, doi.org/10.1353/wp.2007.0004.


Downes, Targeting Civilians in War.


James D. Morrow, “When Do States Follow the Laws of War?” American Political Science Review, Vol. 101, No. 3 (August 2007), pp. 559–572, doi.org/10.1017/S000305540707027X.


On the development of such strategies, see Tanisha M. Fazal, “Why States No Longer Declare War,” Security Studies, Vol. 21, No. 4 (2012), pp. 557–593, doi.org/10.1080/09636412.2012.734227. On adopting creative interpretations, see Neta C. Crawford, Accountability for Killing: Moral Responsibility for Collateral Damage in America's Post-9/11 Wars (Oxford: Oxford University Press, 2013); and Ian Hurd, How to Do Things with International Law (Princeton, N.J.: Princeton University Press, 2017).


This assumption is contested. See Lawrence R. Jacobs and Robert Y. Shapiro, Politicians Don't Pander: Political Manipulation and the Loss of Democratic Responsiveness (Chicago: University of Chicago Press, 2000).


This metric is often used by scholars interested in norm strength or norm decline. See, for example, Ryder McKeown, “Norm Regress: U.S. Revisionism and the Slow Death of the Torture Norm,” International Relations, Vol. 23, No. 1 (March 2009), pp. 5–25, doi.org/10.1177/0047117808100607.


Sagan and Valentino, “Revisiting Hiroshima in Iran.”


See Matthew J. Belvedere, “Trump Asks Why U.S. Can't Use Nukes: MSNBC,” CNBC, August 3, 2016, https://www.cnbc.com/2016/08/03/trump-asks-why-us-cant-use-nukes-msnbcs-joe-scarborough-reports.html; and Tom LoBianco, “Donald Trump on Terrorists: ‘Take Out Their Families,‘” CNN, December 3, 2015, https://www.cnn.com/2015/12/02/politics/donald-trump-terrorists-families/index.html.


For example, see Elliott Kaufman, “The Nuclear Taboo Is Weaker Than You Think,” National Review, August 10, 2017, https://www.nationalreview.com/2017/08/nuclear-weapons-taboo-breaking-majority-americans-support-save-troops-lives-conventional-warfare/; and Ryan Pickrell, “Americans Wouldn't Really Mind if We Just Nuked Somebody,” Daily Caller, August 4, 2017, https://dailycaller.com/2017/08/04/americans-wouldnt-really-mind-if-we-just-nuked-somebody/.


Thomas, The Ethics of Destruction; Vaughn P. Shannon, “Norms Are What States Make of Them: The Political Psychology of Norm Violation,” International Studies Quarterly, Vol. 44, No. 2 (June 2000), pp. 293–316, doi.org/10.1111/0020-8833.00159; Mantilla, “Social Pressure and the Making of Wartime Civilian Protection Rules”; Michelle Jurkovich, “What Isn't a Norm? Redefining the Conceptual Boundaries of ‘Norms’ in the Human Rights Literature,” International Studies Review, published ahead of print, August 16, 2019, doi.org/10.1093/isr/viz040; and Richard M. Price and Nina Tannenwald, “Norms and Deterrence: The Nuclear and Chemical Weapons Taboos,” in Peter J. Katzenstein, ed., The Culture of National Security: Norms and Identity in World Politics (New York: Columbia University Press, 1996), pp. 114–152.


Legro, “Which Norms Matter?”


Kreps, “Flying under the Radar”; Wallace, “International Law and Public Attitudes toward Torture”; Kreps and Wallace, “International Law, Military Effectiveness, and Public Support for Drone Strikes”; Chilton, “The Laws of War and Public Opinion”; Chilton and Versteeg, “International Law, Constitutional Law, and Public Support for Torture”; Horowitz, “Public Opinion and the Politics of the Killer Robots Debate”; and Kevin L. Young and Charli Carpenter, “Does Science Fiction Affect Political Fact? Yes and No: A Survey Experiment on ‘Killer Robots,‘” International Studies Quarterly, Vol. 62, No. 3 (September 2018), pp. 562–576, doi.org/10.1093/isq/sqy028.


As Adam Chilton notes, this is a flaw in many studies of international law effects, which therefore cannot distinguish between the effect of extant international law knowledge and the effect of international law information/priming through a survey treatment. Chilton, “The Laws of War and Public Opinion,” p. 18.


Friedrich Kratochwil and John Gerard Ruggie, “International Organization: A State of the Art on an Art of the State,” International Organization, Vol. 40, No. 4 (Autumn 1986), pp. 753–775, doi.org/10.1017/S0020818300027363.


Gartner, “The Multiple Effects of Casualties on Public Support for War”; Conrad et al., “Threat Perception and Public Support of Government Torture”; and Horowitz, “Public Opinion and the Politics of the Killer Robots Debate.”


See Thomas M. Dolan, “Unthinkable and Tragic: The Psychology of Weapons Taboos in War,” International Organization, Vol. 67, No. 1 (January 2013), pp. 37–63, doi.org/10.1017/S0020818312000379. Sagan and Valentino themselves cite Gallup polls from World War II in stating that “U.S. public support for killing enemy civilians on a large scale with chemical weapons increased when subjects were cued that using such weapons would save the lives of U.S. soldiers.” Sagan and Valentino, “Revisiting Hiroshima in Iran,” p. 61.


Chaim Kaufmann, “Threat Inflation and the Failure of the Marketplace of Ideas: The Selling of the Iraq War,” International Security, Vol. 29, No. 1 (Summer 2004), pp. 5–48, doi.org/10.1162/0162288041762940; Ido Oren and Ty Solomon, “WMD: The Career of a Concept,” New Political Science, Vol. 35, No. 1 (2013), pp. 109–135, doi.org/10.1080/07393148.2012.754683; and Iran Watch, “The Iraq War's Impact on Nonproliferation” (Washington, D.C.: Wisconsin Project on Nuclear Arms Control, April 14, 2004), https://www.iranwatch.org/our-publications/roundtable/iraq-wars-impact-nonproliferation.


Kendall Breitman, “Poll: Half of Republicans Still Believe WMDs Found in Iraq,” Politico, January 7, 2015, https://www.politico.com/story/2015/01/poll-republicans-wmds-iraq-114016.html.


On the use of historical analogies in foreign policy crises, see Robert Jervis, Perception and Misperception in International Politics (Princeton, N.J.: Princeton University Press, 1976); and Yuen Foong Khong, Analogies at War: Korea, Munich, Dien Bien Phu, and the Vietnam Decisions of 1965 (Princeton, N.J.: Princeton University Press, 1992). On analogical reasoning more broadly, see M.J. Peterson, “The Use of Analogies in Developing Outer Space Law,” International Organization, Vol. 51, No. 2 (Spring 1997), pp. 245–274, doi.org/10.1162/002081897550357.


Eric S. Edelman, Andrew F. Krepinevich, and Evan Braden Montgomery, “The Dangers of a Nuclear Iran: The Limits of Containment,” Foreign Affairs, Vol. 90, No. 1 (January/February 2011), pp. 66–81; Matthew Kroenig, “Time to Attack Iran: Why a Strike Is the Least Bad Option,” Foreign Affairs, Vol. 91, No. 1 (January–February 2012), p. 7, https://www.jstor.org/stable/25800382; and Matthew Kroenig, “Still Time to Attack Iran: The Illusion of a Comprehensive Nuclear Deal,” Foreign Affairs, January 7, 2014, https://www.foreignaffairs.com/articles/middle-east/2014-01-07/still-time-attack-.


“37% Call for U.S. Military Action against Iran” (Asbury Park, N.J.: Rasmussen Reports, July 27, 2018), http://www.rasmussenreports.com/public_content/politics/current_events/iran/37_call_for_u_s_military_action_against_iran.


“73% Say It's Likely Iran Will Develop Nuclear Weapons” (Asbury Park, N.J.: Rasmussen Reports, July 26, 2018), http://www.rasmussenreports.com/public_content/politics/current_events/iran/73_say_it_s_likely_iran_will_develop_nuclear_weapons.


Shannon, “Norms Are What States Make of Them.”


Donald R. Kinder and Lynn M. Sanders, “Mimicking Political Debate with Survey Questions: The Case of White Opinion on Affirmative Action for Blacks,” Social Cognition, Vol. 8, No. 1 (April 1990), pp. 73–103; Justin Lewis, Constructing Public Opinion: How Political Elites Do What They Like and Why We Seem to Go Along with It (New York: Columbia University Press, 2001); Kreps, “Flying under the Radar”; and Alexandria Nylen and Charli Carpenter, “Questions of Life and Death: (De)constructing Human Rights Norms through U.S. Public Opinion Surveys,” European Journal of International Security, Vol. 4, No. 2 (June 2019), pp. 142–162, doi.org/10.1017/eis.2019.3.


Against this proposition (among others), see Robert A. Pape, “Why Japan Surrendered,” International Security, Vol. 18, No. 2 (Fall 1993), pp. 154–201, doi.org/10.2307/2539100; Tsuyoshi Hasegawa, Racing the Enemy: Stalin, Truman, and the Surrender of Japan (Cambridge, Mass.: Belknap, 2005); and Ward Wilson, “The Bomb Didn't Beat Japan … Stalin Did,” Foreign Policy, May 30, 2013, https://foreignpolicy.com/category/analysis/argument/.


There is much evidence to the contrary. See Robert A. Pape, Bombing to Win: Air Power and Coercion in War (Ithaca, N.Y.: Cornell University Press, 1996); Caleb Carr, The Lessons of Terror: A History of Warfare against Civilians, rev. ed. (New York: Random House, 2003); and Evangelista and Shue, The American Way of Bombing.


Sagan and Valentino do explore another variant of the nuclear scenario, a third option of keeping the ayatollah, which dropped support for a nuclear strike from 56 percent to 40 percent. Sagan and Valentino, “Revisiting Hiroshima in Iran,” p. 70.


See online appendix at doi.org/10.7910/DVN/QE1AW5.


See Sagan and Valentino, “Revisiting Hiroshima in Iran,” p. 57. When we use “support” in this article, we are referring to our (and their) findings on “prefer” rather than “approve.”


Geoffrey P.R. Wallace, “Condemning or Condoning the Perpetrators? International Humanitarian Law and Attitudes toward Wartime Violence,” Law & Social Inquiry, Vol. 44, No. 1 (February 2019), pp. 192–226, doi.org/10.1017/lsi.2018.22.


Chilton, “The Laws of War and Public Opinion,” p. 18.


It is possible, however, that the strength of positive responses to this question reflects social desirability bias. See Ivar Krumpal, “Determinants of Social Desirability Bias in Sensitive Surveys: A Literature Review,” Quality & Quantity, Vol. 47, No. 4 (June 2013), pp. 2025–2047, doi.org/10.1007/s11135-011-9640-9. We argue that this is an appropriate way to capture the intersubjective strength of a social norm, which is triggered primarily in relation to socially constructed expectations of what Americans believe the normatively “right” answer is. In other words, even if this is not a good measure of respondents' individual moral beliefs, it is still a good measure of the strength of an intersubjective norm precisely because surveys are, to some degree, conversational settings in which intersubjective beliefs may be present. On the difference between moral principles and norms, see Jurkovich, “What Isn't a Norm?”


We follow Sagan and Valentino by asking that all scenarios be rated from 1 to 6 (1 meaning “strongly prefer to continue ground war” and 6 meaning “strongly prefer to launch strike”), then collapse our data to a binary “% prefer strike” and test the difference in means. Testing the difference using raw scores does not change the statistical significance of any results.


Results from treatment group 6, n = 250, p = 0.074. For replication data, see online appendix.


Except for the replication, we used a version of the article title and question that referred to “Iranian civilians” rather than an “Iranian city” to ensure that participants would know that the civilian deaths were intentional rather than collateral. Doing so allowed us to separate out the civilian immunity norm from the norm of proportionality. This change alone, however, did not result in a significant decrease in support.


Results from combining treatment groups 1 and 2, n = 500, p = 1.3e-07.


This analysis reflects survey-weighted answers of all groups (1–9) that received the ethical norm question (n = 2250). Sixty-one percent strongly agreed, 19 percent somewhat agreed, 6.9 percent somewhat disagreed, 2.8 percent strongly disagreed, and 10 percent were not sure. For those that received the question after the Iran scenario question, “somewhat or strongly agree” averaged 77 percent (groups 1–6, n = 1500), while those that were asked before the question averaged 85 percent (groups 7–9, n = 750).


This finding is based on coding treatment group 7, where the respondents received this question before they received any other questions.


Even the minority of respondents who somewhat or strongly disagreed that it is wrong to target civilians exhibited ambivalence to do so: of the two groups that “strongly disagreed” (a mere .09 percent of those who left a comment in this treatment group), one “explained” their answer by saying, “The population should not be involved.”


Shannon, “Norms Are What States Make of Them.”


This result reflects survey-weighted answers from groups 1 + 2 combined (n = 500) that received the ethical norm question after the scenario so as to avoid ethical priming effects on strike support. Fifty-six percent in these groups strongly agreed with the ethical norm, as opposed to 61 percent across all groups (1–9, n = 2250) that were asked the question. Surprisingly, 80 percent of those who only somewhat agreed with the ethical norm supported the strike, which is the same rate as those who somewhat disagreed.


Note that when we compare ethical priming (treatment group 7, n = 250, 46 percent support) with our scenario with “civilians” in the title (treatment groups 1 + 2, n = 500, 54 percent support), p = 0.07. If we instead compare ethical priming with our original replication (treatment group 6, n = 250, 57 percent support), p falls to 0.023.


Kahl, “In the Crossfire or the Crosshairs?”; Crawford, Accountability for Killing; Kreps, “Flying under the Radar”; Chilton, “The Laws of War and Public Opinion”; and Bruce Cronin, Bugsplat: The Politics of Collateral Damage in Western Armed Conflicts (New York: Oxford University Press, 2018).


With two student coders, one of the researchers conducted a grounded theory analysis of all the comments to develop a code list with code definitions. These were applied independently by at least two coders to all of the comments, through a series of coding waves designed to refine code definitions and improve inter-rater reliability. Ultimately, the average inter-rater reliability across this set of codes between the two coders was slightly higher than 90 percent. The principle investigator adjudicated mismatched codes to arrive at a final frequency distribution, reverting to a consensus coding process on ambiguous cases. Cases can produce multiple codes.


Notably, this is based on a very liberal code definition for “strike city.” We included not only comments where the respondent literally said to strike the city but also all those in which they leaned against the ground war but did not suggest an alternative option.


It must be noted that a few of the suggested “alternative options” would also violate humanitarian law, such as creating a blockade to “starve them out” or using cyberwarfare to “bring life in Iran to a halt.”


See also Rathbun and Stein, “Greater Goods.”


Thomas Risse, “‘Let's Argue!‘: Communicative Action in World Politics,” International Organization, Vol. 54, No. 1 (Winter 2000), pp. 1–39, doi.org/10.1162/002081800551109.


Indeed, we suspect this may be a feature of much other experimental work on the laws of war, which may be discounting the likely impacts of international laws and norms by design.


James G. March and Johan P. Olsen, “The Institutional Dynamics of International Political Orders,” International Organization, Vol. 52, No. 4 (Autumn 1998), pp. 943–969, doi.org/10.1162/002081898550699.


Sagan and Valentino, “Revisiting Hiroshima in Iran,” p. 76.


Carpenter, “Innocent Women and Children”: Gender, Norms, and the Protection of Civilians; and Kinsella, The Image before the Weapon.


Kahl, “In the Crossfire or the Crosshairs?”; Crawford, Accountability for Killing; and Cronin, Bugsplat.


John Zaller and Stanley Feldman, “A Simple Theory of the Survey Response: Answering Questions versus Revealing Preferences,” American Journal of Political Science, Vol. 36, No. 3 (August 1992), pp. 579–616, doi.org/10.2307/2111583; and George F. Bishop, Robert W. Oldendick, and Alfred Tuchfarber, “What Must My Interest in Politics Be If I Just Told You ‘I Don't Know’?” Public Opinion Quarterly, Vol. 48, No. 2 (Summer 1984), pp. 510–519, doi.org/10.1086/268846.


Martha Finnemore and Kathryn Sikkink, “International Norm Dynamics and Political Change,” International Organization, Vol. 52, No. 4 (Autumn 1998), pp. 887–917, doi.org/10.1162/002081898550789; McKeown, “Norm Regress”; and Diana Panke and Ulrich Petersohn, “Norm Challenges and Norm Death: The Inexplicable?” Cooperation and Conflict, Vol. 51, No. 1 (March 2016), pp. 3–19, doi.org/10.1177/0010836715597948.


Sagan and Valentino, “Revisiting Hiroshima in Iran,” p. 45.


Rufus E. Miles Jr., “Hiroshima: The Strange Myth of Half a Million American Lives Saved,” International Security, Vol. 10, No. 2 (Fall 1985), pp. 121–40, doi.org/10.2307/2538830; and Barton J. Bernstein, “The Atomic Bombings Reconsidered,” Foreign Affairs, Vol. 74, No. 1 (January/February 1995), pp. 135–152, doi.org/10.2307/20047025.


Thomas, The Ethics of Destruction; Tannenwald, The Nuclear Taboo; and Sahr Conway-Lanz, “Bombing Civilians after World War II: The Persistence of Norms against Targeting Civilians in the Korean War,” in Evangelista and Shue, The American Way of Bombing, pp. 47–63.


Jean-Marie Henckaerts and Louise Doswald-Beck, eds., Customary International Humanitarian Law, Vol. 1: The Rules (Cambridge: Cambridge University Press and ICRC, 2005).


Rebecca Davis Gibbons, “The Humanitarian Turn in Nuclear Disarmament and the Treaty on the Prohibition of Nuclear Weapons,” Nonproliferation Review, Vol. 25, Nos. 1–2 (February/March 2018), pp. 11–36, doi.org/10.1080/10736700.2018.1486960.


Indeed, it is questionable that the Joint Chiefs of Staff (JCS) would ever offer saturation bombing as an option in the real world. See Kahl, “In the Crossfire or the Crosshairs?” The fictional and highly unrealistic imprimatur of the JCS in the vignette, in which the JCS purportedly propose this option with no concerns about legality, may have been an additional factor cueing respondents to believe the strike would be legal.


Nylen and Carpenter, “Questions of Life and Death.”


Kreps, “Flying under the Radar,” p. 4.


Kinder and Sanders, “Mimicking Political Debate with Survey Questions”; and Lewis, Constructing Public Opinion.


See Kreps and Wallace, “International Law, Military Effectiveness, and Public Support for Drone Strikes.”


Risse, “‘Let's Argue!‘”


On public opinion surveys as conversational settings, see Lisbeth Lipari, “Toward a Discourse Approach to Polling,” Discourse Studies, Vol. 2, No. 2 (May 2000), pp. 187–215, doi.org/10.1177/1461445600002002003.


Andrew P. Cortell and James W. Davis Jr., “How Do International Institutions Matter? The Domestic Impact of International Rules and Norms,” International Studies Quarterly, Vol. 40, No. 4 (December 1996), pp. 451–478, doi.org/10.2307/2600887; and Simmons, Mobilizing for Human Rights.


Kreps and Wallace, “International Law, Military Effectiveness, and Public Support for Drone Strikes.”


Lewis, Constructing Public Opinion; Kreps, “Flying under the Radar”; and Nylen and Carpenter, “Questions of Life and Death.”


Dan De Luce, “Cruz Says the U.S. ‘Carpet Bombed’ in the Gulf War. It Didn't,” Foreign Policy, February 8, 2016, https://foreignpolicy.com/2016/02/08/cruz-says-the-u-s-carpet-bombed-in-the-gulf-war-it-didnt/.


Gibbons, “The Humanitarian Turn in Nuclear Disarmament and the Treaty on the Prohibition of Nuclear Weapons.”


Jamal Barnes, “The ‘War on Terror’ and the Battle for the Definition of Torture,” International Relations, Vol. 30, No. 1 (March 2016), pp. 102–124, doi.org/10.1177/0047117815587775.