Psychological Barriers to Resolving Intergroup Conflict: An Extensive Review and Consolidation of the Literature

Intergroup conflict is ubiquitous and has plagued relationships between families, tribes, cultures, sects, ethnic groups, and states since well before the dawn of “civilization” (Ferguson 2008; White 2009; Pinker 2011; Harari 2014). At its most benign, intergroup conflict manifests as social distance and encourages competition over status and economic resources. At its worst, it fuels hatred and misdeeds, incites violence, and gives rise to protracted armed conflicts and even genocide. While the structural causes of conflict vary (Deutsch 2006)—with some conflicts arising from competition over scarce economic resources, and others stemming from ideological, religious, or political rivalry—intergroup conflicts also appear to exhibit a psychological dimension, consisting of attitudes, emotions, biases, and beliefs, which complicates the task of resolving such conflicts. These “psychological barriers” to conflict resolution not only render purely structural solutions insufficient, they reduce the motivation of conflicting parties to consider solutions at all. Hence, while it remains crucial to evaluate and address the structural impediments to conflict resolution (Raiffa 1982; Nadler 2012; Bachar and Weiner 2014; Crump 2015; Ditlmann, Samii, and Zeitzoff 2017), it is equally important to understand—and identify ways to attenuate—psychological barriers (Ross and Ward 1995; Kelman 2008).

In this article, we (1) review the vast literature that has identified psychological barriers to intergroup conflict resolution, (2) consolidate this research to produce a tractable list of “unique” psychological barriers, (3) categorize these barriers according to whether they represent cognitive, affective, or motivational psychological states, (4) employ a data visualization tool to illustrate the relationship between barriers as measured by the extent to which different psychological barriers have been studied conjointly by scholars, (5) catalog empirical work that attempts to attenuate such barriers, and (6) discuss how future efforts among scholars and practitioners might build on the existing research.

Over the years, a significant body of literature has developed on psychological barriers to conflict resolution (Ross and Ward 1995; Kelman 2008; Bruneau and Saxe 2010; Bar‐Tal 2013; Bachar and Weiner 2014; Halperin 2016; Sherman, Brookfield, and Ortosky 2017). Intergroup conflict is a multidimensional phenomenon with a variety of causes, including historical grievances, unequal distribution of power and other resources, competing visions for the future, and incompatible ideologies (Bar‐Tal 2013; Klar and Branscombe 2016). However, the literature on psychological barriers has observed that intergroup conflicts, whatever their root causes, are sustained and exacerbated by psychological mechanisms that inhibit resolution.

While psychological barriers reside in the minds of individuals (Kahneman and Tversky 1995; Ross and Ward 1995), when these attitudes or beliefs are widely shared among group members, they can influence intergroup behaviors through a variety of channels. These pathways range from leader selection, to defining the scope of what is and is not negotiable, to normalizing extreme individual sacrifice, to delegitimizing moderation or compromise in negotiations (Bruneau and Saxe 2010; Bar‐Tal 2013; Bachar and Weiner 2014).

Moreover, psychological barriers are implicated at every stage of intergroup conflict (Bar‐Tal 2013). Some barriers (e.g., anger, fixed‐pie perceptions, and confirmation bias) might help instigate conflicts; others (e.g., moral amplification, dehumanization, and self‐identity threat) can fuel existing conflicts; still others (e.g., fear, loss aversion, and the emergence of sacred values) might make efforts to resolve conflict less attractive and/or less effective. Indeed, some psychological barriers might be operative at every stage.

The literature on psychological barriers to conflict resolution, although rich, is diffuse. As we describe below, our initial review uncovered eighty different psychological barriers that scholars have identified. This speaks both to the magnitude of the problem that researchers and practitioners must face, as well as to the seeming impracticality of resolving it. If would‐be contributors to this literature, or would‐be conflict resolution practitioners in the field, must understand, evaluate, and tackle this number of psychological barriers, there is little hope of meaningful progress.

Given the considerable attention that this topic has garnered from scholars—and the great relevance of this subject to practitioners and policy makers—this article audits the existing literature and creates a more organized and tractable list of psychological barriers to intergroup conflict resolution. We then review and organize the empirical research that has attempted to attenuate psychological barriers, identifying the different methods that have been used, and examining which methods have been targeted at which types of psychological barriers. While prior research has featured partial reviews of psychological barriers and interventions aimed at reducing such barriers (see Hameiri and Halperin 2015; Ditlmann, Samii, and Zeitzoff 2017), none, to our knowledge, has attempted an exhaustive cataloguing of psychological barriers or barrier‐reducing psychological interventions.

To create an exhaustive list of the psychological barriers to conflict resolution that have been identified by scholars, we conducted a systematic literature review using Brown University’s journal database (through EBISCO), Harvard University’s HOLLIS catalog, the PsycInfo database, and Google Scholar. To do so, we used the following search terms: “psychological barriers,” “cognitive barriers,” “barriers,” “biases,” “intergroup conflict,” “conflict,” “intergroup disputes,” “disputes,” “peace,” “peacemaking,” “intractable conflict,” and “negotiation.” We first placed each of these terms into one of two categories: those referring to barriers (which included “psychological barriers,” “cognitive barriers,” “barriers,” and “biases”) and those referring to conflict (“intergroup conflict,” “conflict,” “intergroup disputes,” “disputes,” “peace,” “peacemaking,” “intractable conflict,” and “negotiation”). We then paired each term in the barriers list with every term in the conflict list, thereby creating thirty‐two pairs of search terms. These thirty‐two items (e.g., “psychological barriers AND intergroup conflict,” “psychological barriers AND conflict,” “biases AND negotiation”) comprised the full set of items we used to search for articles in the aforementioned databases.

This process yielded seventy‐nine unique articles published as far back as the mid‐twentieth century. Then, to ensure a sufficiently comprehensive search of the literature, we examined the reference list of each of these articles to identify any additional articles that might be relevant to our review, but which were overlooked by our search criteria. Finally, we examined the literature cited in every article to find the earliest article cited for each psychological barrier. For our purposes, this amounted to identifying the first article in which a barrier was discussed or studied in the context of conflict, negotiation, or stereotyping.¹ We employed a saturation method (Glaser and Strauss 1967) to determine when to conclude the search. On each search query, we considered that we had reached the saturation point when we hit a succession of five pages of search results (with ten search results per page) that failed to turn up any new article that discussed psychological barriers. Upon hitting this point, we would move on to the next set of search terms. We replicated this process in each of the four databases we used (Brown’s database, Harvard’s database, PsycInfo, and Google Scholar). Because the number of relevant results varied by search term, and also successive search queries would typically yield a diminishing number of “unique” articles (i.e., those which had not been found in previous searches), the total number of articles evaluated differed for each search query.

In the end, we collected a total of 140 unique articles or book chapters. This included articles that contained lists, of varying sizes, of psychological barriers (e.g., Wade‐Benzoni et al. 2001; Thompson and Lucas 2014), as well as articles that identified or discussed one specific barrier (e.g., Kennedy and Pronin 2008; Ginges and Atran 2013; Young and Sullivan 2016). One of the authors then read every article and created a comprehensive list of every unique psychological barrier mentioned in the text. Initially, every barrier that was worded (i.e., phrased) differently was entered as a separate entry. For example, while “loss aversion” and “concession aversion” are hard to distinguish conceptually, we kept them separate at this stage. We did the same with mechanistically related barriers such as “bias perception” and “naïve realism”; these were listed separately because it has been argued that the former is merely a consequence of the latter (Ross and Ward 1995); others have considered “bias perception” to be its own phenomenon (Kennedy and Pronin 2008).

One reason for the conceptual redundancies appears to be the clustering‐by‐discipline nature of this research, a phenomenon we described earlier. For example, Bazerman and Neale’s 1983 article, which focuses on negotiation, uses the term “fixed‐pie bias” to describe the tendency of disputants to believe that there are no opportunities for mutual benefit because one side can only gain to the extent the other loses. Four years later, Kelman’s 1987 article identifies the same tendency in international conflicts but refers to it as a “view of the conflict as zero sum.” The limited attention given to work by scholars working on similar problems in different fields or disciplines, while to some extent understandable, undoubtedly contributes to the proliferation of terminology and conceptualizations beyond what is helpful or tractable.

Consequently, our initial list of barriers consisted of eighty separate entries. This list, which we will refer to as our Comprehensive List of psychological barriers, is included in Appendix  A.

To consolidate the eighty barriers, we first combined what appeared to be redundant entries (e.g., “loss aversion” and “concession aversion” became loss aversion; “egocentric bias” and “double standard” became egocentric perceptions). This consolidation effort, whereby we discarded barriers that were conceptually identical (or highly similar) to others, resulted in the shortening of our list from eighty barriers to forty‐eight distinct psychological barriers.

Finally, in order to create an even more coherent and tractable list of psychological barriers for use by academics and practitioners, we took the additional step of combining barriers that were described as stemming from (or manifesting) the same proximate underlying psychological mechanism. For example, the “fixed‐pie bias” and “reactive devaluation,” while initially identified as separate barriers, were integrated in this stage. While these barriers might be conceptually distinct, they both rest on the presumption (or bias) that “if it is good for them, it must be bad for us”; as a result, we subsumed “reactive devaluation” under the term fixed‐pie perceptions. This final round of consolidation resulted in a final list of twenty‐six unique psychological barriers to intergroup conflict resolution.

Table One provides an inventory and descriptions of the twenty‐six unique psychological barriers and shows how each of the forty‐eight distinct psychological barriers is classified therein. Each citation in the table refers to the earliest article we encountered during our review that referred to the psychological barrier in the context of negotiation or conflict.

To further organize our list of twenty‐six unique barriers, we created a typology based on research that distinguishes between the cognitive, affective, and motivated reasoning determinants of attitudes and beliefs (Kahneman and Tversky 1995; Halperin 2016; Sherman, Brookfield, and Ortosky 2017). Consistent with these proposed distinctions, our review of the literature on psychological barriers found that some scholars (e.g., Kahneman and Tversky 1995; Ross and Ward 1995) focused on “cognitive barriers,” while a second group (e.g., Halperin 2011; Halperin 2016) focused exclusively on emotion‐related barriers to conflict resolution, and a third group (e.g., Sherman et al. 2007; Binning et al. 2010; Sherman, Brookfield, and Ortosky 2017) emphasized the role that self‐enhancement might play in the creation of attitudes that promote positive self (or group) image at the cost of fueling intergroup conflict. Accordingly, we classified each of our twenty‐six unique barriers based on whether scholars had most strongly associated it with underlying psychological processes that were cognitive, affective, and/or motivated in nature. We also considered the possibility that more than one of these dimensions—cognitive, affective, and motivated—might be implicated in the case of a psychological barrier.

The first category in this typology, “cognitive barriers,” consists of conflict‐enhancing perspectives and beliefs that arise from cognitive limitations, heuristics, and biases (Kahneman and Tversky 1995; Ross and Ward 1995). Cognitive barriers include psychological phenomena such as fixed‐pie perceptions and failures of perspective taking. The research on these barriers is strongly rooted in work on heuristics and cognitive biases—such as the foundational studies conducted by Kahneman and Tversky in the 1970s and 1980s, as well as extensive work by cognitive and social psychologists (and more recently, by behavioral economists). These barriers are often implicated in explanations for why negotiation attempts fail—or end with suboptimal outcomes.

The second category, “affective barriers,” consists of attitudes and emotions (typically, negative emotions targeted at members of the out‐group) that discourage or interfere with intergroup conflict resolution (Halperin 2016). Affective barriers include emotions such as anger, fear, and hatred. Perhaps because protracted violent conflicts tend to involve higher magnitudes of emotion than do other intergroup conflicts, much of the research on affective barriers stems from work on intractable conflicts (e.g., Israel–Palestine or the Balkans). Notably, the emotions implicated in these conflicts can result from underlying cognitive appraisals; hatred, for example, might stem at least in part from the belief that the out‐group is inherently malevolent and will never change (Levontin, Halperin, and Dweck 2013; Halperin 2016).

The third category, “barriers of motivated reasoning” (hereafter referred to as “motivated barriers”), consists of attitudes and beliefs that arise from, or are exacerbated by, a desire to see oneself (or one’s group) positively (De Dreu and Van Knippenberg 2005; Sherman, Brookfield, and Ortosky 2017). Motivated barriers include psychological phenomena such as confirmation bias and system justification. Such barriers largely entail distorted information processing designed to protect core beliefs about the self or the world, with beliefs about the world sometimes being incorporated into one’s overall sense of self (De Dreu and Van Knippenberg 2005). Motivated barriers are studied extensively in the literatures on negotiations and on intractable conflict (e.g., Porat, Halperin, and Bar‐Tal 2013), but also play a role in the literature on partisan disputes in the United States—for example, on evaluations of presidential candidates by voters (Binning et al. 2010).

It is important to acknowledge that our classification is not the only plausible, nor the definitive, method for assigning psychological barriers across these categories. As we discovered, while some barriers appear to fit comfortably in one specific category—e.g., fixed‐pie perceptions (cognitive), anger (affective), system justification (motivated)—others are less simply classified (e.g., sacred values and dehumanization) and could be reasonably assigned to multiple categories. Consequently, we assigned the psychological barriers to categories using the following methodology. First, both of the authors, working independently, assigned each barrier to one of six categories that seemed to offer the “best fit” based on our interpretation of how scholars had described or conceptualized the barrier: cognitive, affective, motivated, cognitive/affective, cognitive/motivated, or affective/motivated. Then, we compared our classifications and resolved any discrepancies with discussion and through further study of how scholars had treated the barrier in question. In all, five of the twenty‐six barriers required further discussion or additional review; in the other twenty‐one cases (i.e., in 81 percent of cases), the authors’ independent classifications were identical.

Figure One shows how we classified the twenty‐six unique psychological barriers across the cognitive, affective, and motivated reasoning dimensions.

The categorization of barriers across these three dimensions is useful not only because it provides a conceptually sound framework for organizing the literature, but because future research might examine how barriers from different categories could be implicated or relevant in different types or phases of conflicts. For instance, based on our examination of the research on motivated barriers, we speculate that such barriers might be especially implicated in the hesitation of conflicting parties to even engage in negotiations with one another. For example, we might hypothesize that confirmation bias would reduce a group’s ability to acknowledge good faith efforts by the “enemy” to resolve differences, or that moral amplification will reduce the willingness to initiate discussions with those who have perpetrated seemingly “evil” acts (Sande et al. 1989), or that system justification will decrease the appetite for working to change even a destructive status quo.

We also speculate that cognitive barriers, while present in all phases of a conflict, might be especially problematic once negotiations have commenced. For example, loss aversion, failures of perspective taking, and fixed‐pie perceptions have often been implicated in the inability of negotiators to identify and reach mutually beneficial agreements (Malhotra and Bazerman 2007), and perceptions of the conflict as unique might prevent participants from seeking to learn lessons from how other conflicts were resolved.

Emotional barriers, meanwhile, might play a predominant role in the aftermath of even “successful” efforts at resolving disputes, especially as groups attempt reconciliation and the normalization of relationships. For example, anger might lead group members to reject negotiated agreements when put to a referendum (Matanock and García‐Sánchez 2017). Even after the fighting has ended, fear might limit interaction between groups and lead each side to invest too little in safeguarding the hard‐fought peace because renewed conflict is considered likely (Riek, Mania, and Gaertner 2006; Wohl and Tabri 2016).

Increased scholarly attention to when—and not just how—psychological barriers are most likely to impact intergroup conflicts could be of tremendous benefit. The current state of the literature, however, is that most of the existing research is organized neither by type (cognitive, affective, and motivated) nor by phase of conflict. As suggested earlier and discussed in more detail in the next section, our review of the literature suggests that prior work on psychological barriers is instead clustered according to the broader research focus and approach of scholars—with much of the work residing in one of four different research domains.

In the process of identifying and consolidating the different psychological barriers, we observed that many of the barriers appeared to cluster together in one of four meaningfully distinguishable research domains (i.e., bodies of work with distinct foci). We report our observation on this briefly here, as we did not have any a priori expectations or planned analyses regarding such clustering.

The first domain relates to research that we might broadly describe as work on social cognition. This body of research, exemplified by the work of Cikara et al. (2014); Kteily, Hodson, and Bruneau (2016); and Bruneau, Kteily, and Falk (2017), focuses primarily on how individuals view other groups. Some of the barriers in this domain are dehumanization (Gubler et al. 2015; McDonald et al. 2016; Kteily and Bruneau 2017; Bruneau, Jacoby et al. 2018), prejudice (Er‐Rafiy and Brauer 2012; De Freitas and Cikara 2017; Kteily et al. 2017; Orosz et al. 2018), and failures of perspective taking at the intergroup level, as when people exhibit lower empathy for out‐group versus in‐group members (Saguy and Kteily 2011; Cikara et al. 2014; Zaki and Cikara 2015; Bruneau, Cikara, and Saxe 2017).

The second research domain focuses on cognitive biases and heuristics in negotiations and disputes. Examples include the work of Bazerman and Neale (1983), Kahneman and Tversky (1995), and Ross and Ward (1995). Although this work is applicable to larger groups (e.g., Kelman 2008; Gayer et al. 2009), the emphasis tends to be on individual and interpersonal decision‐making in the context of negotiation and conflict. The barriers most often encountered in this domain are loss aversion (Bazerman, Magliozzi, and Neale 1985; Kahneman and Tversky 1995; Gayer et al. 2009), fixed‐pie perceptions (Bazerman and Neale 1983; Ross and Stillinger 1991; De Dreu, Koole, and Steinel 2000), and failures of perspective taking such as naïve realism and the illusion of transparency (Griffin and Ross 1991; Hunter, Stringer, and Watson 1991; Ross and Ward 1995; Lawson and Miller 1996; Van Boven, Gilovich, and Medvec 2003).

The third research domain we identified focuses on group level affect and cognition. This research, as in the work of Bar‐Tal (2013); Cohen‐Chen, Crisp, and Halperin (2015); and Halperin (2016), focuses on attitudes, emotions, and beliefs held collectively by groups (Bar‐Tal 2013). The barriers that are most frequently discussed among these scholars are competing narratives (Auerbach 2010; Nasie et al. 2014; Hameiri and Nadler 2017), collective emotions (Cehajić‐Clancy et al. 2011; Halperin et al. 2014; Halperin 2016), and perceptions of the conflict as unique (Cohen‐Chen, Crisp, and Halperin 2015; Kudish, Cohen‐Chen, and Halperin 2015). Notably, much of this research is rooted in the context of the Israeli–Palestinian conflict, although it has been applied to a variety of other protracted conflicts and post‐conflict settings, such as Colombia (Orozco et al. 2008) and the former Yugoslavia (Cehajić‐Clancy et al. 2011). It has also been applied to intergroup relations in societies at peace, as in work on competitive victimhood that looks at attitudes among white Americans toward affirmative action policies in the United States (Young and Sullivan 2016).

The fourth research domain is comprised of research on values and identity. This research includes work such as Steele (1988), Ginges and Atran (2013), and Sherman, Brookfield, and Ortosky (2017). Here we find research on barriers such as self‐identity threat (Cohen, Aronson, and Steele 2000; Binning et al. 2015; Sherman, Brookfield, and Ortosky 2017) and sacred values (Baron and Spranca 1997; Ginges et al. 2007; Ginges and Atran 2013). This literature focuses not only on violent intergroup conflict, but also nonviolent political conflict, such as the divide between conservatives and liberals in the United States (e.g., Cohen et al. 2007; Graham, Haidt, and Nosek 2009; Binning et al. 2010, 2015).

While not all of the research on psychological barriers fits neatly into this (or any) categorization, the presence of seemingly different, clustered research agendas suggests both the diversity of approaches that scholars have taken to examine the psychology of intergroup conflict as well as the possibility of covariance among certain types of barriers. Subsets of psychological barriers might not only co‐occur at different phases of the conflict, as suggested in the previous section, but they might also interact in other ways (e.g., covary or be sequentially or causally linked) across different types of conflict. Later in this article we revisit our call for future research to examine the possibility of targeting “portfolios” of barriers.

Thus far we have described two ways in which the research on psychological barriers might be organized. The first, a largely deductive exercise, involved our assignment of barriers across the cognitive, affective, and motivated categories. The second, involving more causal empiricism, revealed that the barriers appear to be cluster based on the research interests of scholars working in one of four research domains.

Here we consider a more careful and rigorous inductive approach to understanding the ecosystem of research on psychological barriers. Specifically, we sought to analyze how closely each psychological barrier is associated with every other psychological barrier in the work being done by scholars. We did so by conducting a network analysis that uses as its feedstock the number of times each pair of barriers appears within the same research article, with our complete reference section providing the sample for this analysis.

To accomplish this, one author reread each of the 140 relevant articles and book chapters that discussed psychological barriers in our reference section and coded it for the presence (or absence) of any mention of each of the twenty‐six unique psychological barriers (by searching for any of the forty‐eight distinct terms that are subsumed therein). Articles or books that did not focus on psychological barriers (e.g., Harari 2014) were excluded from the analysis. We then counted the number of co‐occurrences that existed for every pair of barriers. For example, if an article mentioned fear and confirmation bias only, it increased (by one) the count of co‐occurrences between these two barriers. If four barriers (e.g., A, B, C, and D) were mentioned in an article, the count would increase by one for each of the six pairs of barriers that these four barriers yield (AB, AC, AD, BC, BD, and CD). We used these data to produce a visual network showing the extent to which the barriers are linked to each other. The number of co‐occurrences between barriers determines the thickness of the link between them, with thicker links between barriers that appear together more frequently in scholarly work. The total number of times a barrier co‐occurs with (all) other barriers determines the size of the node, with larger circles for those barriers that have a greater number of connections.

Figure Two yields a number of interesting insights. First, the figure shows that barriers are relatively more likely to be studied conjointly when they are of the same type (cognitive, affective, or motivated) than when they differ across this categorization. This is especially true in the case of research on affect, where there is very strong connectivity between three of the four “purely” affective barriers: hatred, fear, and anger. When looking between categories, the figure reveals that there are more cognitive‐affective links and cognitive‐motivated links than there are links between affective and motivated barriers. This might speak to the possibility that there are cognitive underpinnings to affective states as well as to the phenomenon of motivated reasoning, but that affect and motivated reasoning are less closely related.

The total number of co‐occurrences varies widely across barriers, from a low of 6 (omission bias) to a high of 141 (failures of perspective taking), with a mean of 72.2 total co‐occurrences (median = 74.5). One interpretation for the centrality of failures of perspective taking in our analysis is that it might represent a more foundational barrier that paves the way for others, for example, dehumanization, competing narratives, the delegitimizing of one’s adversary, or egocentric perceptions. Similarly, cognitive misconstruals of the out‐group might be causally linked to anger and fear, in much the same way that some prior research (e.g., Halperin 2016) has linked specific emotions (e.g., hatred) to specific cognitive appraisals of the out‐group. While such interpretations are clearly plausible, our analysis does not provide evidence to support specific explanations for relationships between any pair of barriers; other explanations—ranging from spurious correlations to the idiosyncratic preferences or implicit theories of the scholars who choose what to discuss in their articles—are quite possible.

The figure also shows that certain barriers (e.g., sacred values, system justification, moral amplification, and sunk cost effects) tend not to co‐occur as frequently with specific others, which might suggest that they are indeed more independent or “uncorrelated” barriers, or simply that scholars who study these topics tend to do so in more of a vacuum. Also noteworthy is what the figure does not show, which we might otherwise have anticipated. For example, there is no strong relationship (as measured by scholarly attention in articles) between prejudice and barriers we might have assumed would correspond with it, such as mistrust, fear, or anger. Again, this might speak to the actual relationship between these barriers, or simply to the way in which scholars go about conceptualizing and doing their work.

While much of the research on psychological barriers has sought to identify them or to evaluate their impact, there have also been numerous efforts aimed at identifying the means by which these barriers might be overcome (Gayer et al. 2009; Paluck 2009; Paluck and Green 2009; Shnabel et al. 2009; Bruneau and Saxe 2010; Vasiljevic and Crisp 2013; Hameiri and Halperin 2015; Bruneau, Kteily, and Falk 2017; Hameiri, Bar‐Tal, and Halperin 2019). While many articles (directly or incidentally) provide theoretical or conceptual guidance on how to address the problem of psychological barriers, here we review the empirical literature. More specifically, we reviewed all articles that (a) used an experimental methodology, (b) designed and tested interventions that might attenuate one or more of our forty‐eight distinct psychological barriers, and (c) were situated in the context of intergroup conflict or negotiations.

For this review we leveraged the same databases we had used for identifying our psychological barriers, but this time we created search terms by combining each of the forty‐eight distinct psychological barriers (e.g., “reactive devaluation,” “collective hatred,” and “competitive victimhood”) with the terms “reduce,” “overcome,” “attenuate,” “diminish,” “regulate,” “downregulate,” “upregulate,” “experiment,” and “experimental.” Our search yielded sixty‐two relevant articles.² We used these articles to document every instance in which an experimental design was employed to attenuate one of the psychological barriers we had identified. Remarkably, from among the initial list of forty‐eight barriers, we found forty‐four barriers for which there had been at least one experimental study designed to attenuate it in the context of negotiation or conflict resolution. The only four barriers for which we were unable to find a study that met these criteria—an attempt to attenuate, the use of an experimental method featuring a control group, and the context of intergroup conflict or negotiation—were optimistic overconfidence, omission bias, delegitimization, and system justification.

Across the sixty‐two articles that attempted, experimentally, to address the problem of psychological barriers, we identified five distinct techniques that researchers have tested for doing so. The first technique is awareness, whereby the psychological processes or biases that might be influencing an individual’s attitudes or behavior are made salient. In multiple studies, simply making people aware of a psychological barrier reduced its effects (e.g., Bustamante and Chaux 2014; Nasie et al. 2014). The second technique—contradictory information—was originally suggested by Hameiri and Halperin (2015). In cases where a psychological barrier (e.g., out‐group homogeneity) stems from a false premise (e.g., “all out‐group members are alike”), providing information or data that contradicts this premise might reduce the strength of the psychological barrier. The third technique is redirection. Redirection works by changing an individual’s decision context or attention so that the same psychological processes that were inhibiting conflict resolution are redirected toward promoting it. For example, loss aversion can cause disputants to become intransigent when asked to make costly concessions aimed at resolving conflict (Maoz, Ilan, and Ivri 2007). However, when Gayer et al. (2009) provided information that instead made salient the losses that would accrue from continued conflict, the researchers were able to eliminate the negative effects of loss aversion. The fourth technique is affirmation. Some barriers (e.g., competitive victimhood and competing narratives) entail defensive reactions to information that threatens an individual’s self‐identity or self‐esteem (Sherman and Kim 2005; Shnabel et al. 2013; Simantov‐Nachlieli et al. 2015, 2016; Sherman, Brookfield, and Ortosky 2017). By having people affirm a part of their identities (e.g., remembering a time they lived up to an important value of theirs), it might be possible to make them more resilient in the face of threats to their identity, image, or esteem. For example, Binning and colleagues (2010) were able to reduce levels of political partisanship during the 2008 United States presidential election by having participants write about important personal values. The fifth and final attenuation intervention we found is mindfulness, which is aimed at helping to overcome barriers that are caused by a lack of attention to information or context (e.g., correspondence bias). For example, in a study by Hopthrow et al. (2017), individuals who participated in a short mindfulness exercise demonstrated reduced correspondence bias on an attitude‐attribution paradigm test.

Table Two provides a comprehensive account, based on our review, of which attenuation methods have been used to target twenty‐two of our twenty‐six unique psychological barriers.

We then explored whether different types of attenuation methods might be more or less relevant for targeting different types of psychological barriers. While there is not enough data (i.e., too few articles) to do a rigorous statistical analysis of this possibility, we present our findings in Figure Three, which shows the distribution of attenuation methods across types of psychological barriers (i.e., cognitive versus affective versus motivated). As Figure Three reveals, some types of psychological barriers have been more often targeted by certain types of attenuation methods. For example, contradictory information stands out as the most often attempted technique across all three types of barriers. Bias awareness and affirmation have never been used to attenuate affective barriers, although affirmation is the second most‐utilized attenuation technique with regard to cognitive and motivated barriers.

Many of the articles that focus on techniques for overcoming psychological barriers end with a call for further research on scaling and disseminating these techniques more broadly (e.g., Hameiri and Halperin 2015). Indeed, interventions that have shown promise in lab or field experiments will require scaling if their promise—as tools for influencing large, real‐world conflicts—is to be realized.

Prior work on the scaling of interventions suggests that there is cause for both skepticism and optimism. At a minimum, the creation of consistently effective, evidence‐supported interventions requires painstaking work, with past efforts having required years of pilot testing, data collection, and iterative design (Hameiri, Bar‐Tal, and Halperin 2019). Ditlmann, Samii, and Zeitzoff (2017) have also pointed out that for interventions to have an impact on large‐scale conflict dynamics, they must have a discernable impact on the behavior of individuals, such as increasing in‐group policing, public advocacy, or political action. Simply changing attitudes, beliefs, or emotions, without an impact on relevant behaviors, may be insufficient—and evidence for interventions having behavioral impact is limited (Ditlmann, Samii, and Zeitzoff 2017).

Yet there are examples of barrier reduction techniques that have proven to be robust at various scales (Goldenberg et al. 2018; Hameiri, Bar‐Tal, and Halperin 2019). In addition, while not all attenuation techniques seem equally amenable to successful scaling, a number of the interventions we reviewed could ostensibly be used as seeds for the development of larger‐scale interventions, as was done with the “paradoxical thinking intervention” (Hameiri, Bar‐Tal, and Halperin 2019). Hameiri et al. (2016) developed this intervention into a multimedia ad campaign utilizing billboards, online ads, and fliers to target a small Israeli city. Hawkish Israelis exposed to the campaign reported greater support for compromise and peaceful engagement in the context of the Israeli–Palestinian conflict (Hameiri et al. 2016). This raises the question of which types of interventions would be harder or easier to scale.

Harder‐to‐scale attenuation techniques are the kind that require significant attention and effort by the targets of the intervention—as in the case of guided thought exercises and skills training (Cohen, Aronson, and Steele 2000; Bruneau and Saxe 2012; Bustamante and Chaux 2014; Goldenberg et al. 2016; Bruneau, Kteily, and Falk 2017; Bruneau, Lane, and Saleem 2017). Other techniques, however, require only that participants consider a brief written, visual, or auditory stimulus (Gayer et al. 2009; Halperin et al. 2011; Er‐Rafiy and Brauer 2012; Ginges and Atran 2013; Cohen‐Chen et al. 2014; Bruneau, Cikara, and Saxe 2015; Harth and Shnabel 2015; Wohl et al., 2015; Hameiri et al. 2016; Kimel et al. 2016; Cehajić‐Clancy and Bilewicz 2017; De Freitas and Cikara 2017; Hameiri and Nadler 2017). The latter group represents a class of interventions that is easier to scale and disseminate to influence large audiences.

Existing research suggests at least two ways in which scaling might occur. First, barrier reduction interventions might be disseminated through mass media technology such as online videos, posters, radio or television advertisements, web banners, and leaflets. The works of Hameiri et al. (2016), using a multimedia ad campaign, and Paluck (2009), leveraging a radio drama to implement an intervention, demonstrate the possibility of using media‐based methods to reach large audiences. Second, barrier reduction techniques could be incorporated into content disseminated from the “bully pulpits” of political and social leaders through speeches, communiques, op‐eds, official apologies, dedications, and so on. Roessler’s (2016) study of Yitzhak Rabin’s speeches during the Oslo Process raises the possibility of influencing the beliefs and emotions of large groups of people using such platforms. Future work on scaling attenuation techniques—through these or other methods—would also create a potential venue for scholars and practitioners to collaborate on important issues related to resolving intergroup conflict.

While Ditlmann, Samii, and Zeitzoff (2017) have focused on behaviors that interventions might seek to influence, interventions might also impact intergroup conflict through promoting inaction—as in the case of reduced mobilization and decreased support for would‐be spoilers of conflict resolution efforts. For example, cognitive misconstruals of the out‐group (in particular, perceptions of out‐group homogeneity and collective blame) can be exploited by spoilers during a fragile peace process. Spoilers on one side often take provocative actions knowing that the other side will retaliate—and that the retaliation might be indiscriminate because of collective blame and perceptions of out‐group homogeneity. This can lead to an escalatory spiral of mistrust and hostilities that derails the peace process. Pressman’s (2003) analysis of the outbreak of the Second Intifada in 2000 during the Oslo Process is a paradigmatic example. In the context of already simmering tensions and uncertainty, Ariel Sharon made a visit to the Temple Mount that was widely perceived as provocative. This action fostered widespread Palestinian protests, which the Israelis responded to with massive force. In turn, Palestinian militant groups began a wave of suicide bombings within Israel (Pressman 2003). Interventions that decrease the propensity of groups to engage in collective blame (e.g., Cikara 2015; Bruneau, Kteily, and Falk 2017) or to view the out‐group as a homogeneous entity (e.g., Er‐Rafiy and Brauer 2012) could help take the wind out of the spoiler’s sails.

Finally, another form of “scaling” might entail reaching not a larger group of individuals, but a more influential group of decision makers. Barrier reduction techniques might be incorporated into negotiations between principals, delegations, or key decision makers themselves. For example, beginning a negotiation with mutual recognition of past sufferings (Hameiri and Nadler 2017) to decrease competitive victimhood perceptions, highlighting continued losses from conflict (Gayer et al. 2009) to counteract concession aversion, and even simply making negotiators aware of the existence of psychological barriers such as naïve realism (Nasie et al. 2014) might help make negotiations more productive. Certainly, more research is needed on the impact of such interventions in high‐stakes negotiations and conflicts in situ.

Although this article treats each psychological barrier as an isolated entity—to be understood and tackled without regard to potential covariance with other barriers—in fact, psychological barriers are likely to covary, interact with, and potentially reinforce one another. As an example, the “Ethos of Conflict” framework proposed by Bar‐Tal et al. (2012) conceptualizes an overall ethos, held by societies engaged in intractable conflicts, as a set of eight interconnected beliefs. These include beliefs regarding “the justness of one’s own goals, opponent delegitimization, self‐victimhood, positive self‐image, security, patriotism, unity and peace” (Bar‐Tal 2013: 175). Although Bar‐Tal focused specifically on violent intractable conflicts, similar “portfolios” of psychological barriers are likely to be relevant to other types of conflicts (e.g., nonviolent political conflict, or conflicts between competing ideologies within a society). Consistent with this, our visualization of the literature ecosystem (Figure Two) suggests the possibility that certain barriers might coincide or be causally related.

Future research that takes a “portfolio” approach to studying psychological barriers would be invaluable. For example, scholars might identify specific clusters of barriers that tend to covary, and evaluate which types of portfolios are most or least amenable to attenuation, whether and when targeting individual barriers is effective or efficient, whether some barriers tend to precede (or cause) others, and whether some configurations of psychological barriers are better predictors of how difficult a conflict will be to resolve. It might also emerge that certain interventions can effectively attenuate large clusters of barriers.

This article attempts to provide a comprehensive review of the literature on psychological barriers to intergroup conflict resolution. Our review of over six decades of academic work reveals that the scholars have identified eighty nominally different psychological barriers. With the objective of facilitating future work by scholars and practitioners, we consolidate this research to create a more tractable list of twenty‐six “unique” barriers. We further organize this output with a framework that distinguishes between cognitive, affective, and motivated psychological barriers. We then visualize the ecosystem of research on psychological barriers by showing the extent to which each psychological barrier has been studied conjointly with every other (using the sample of articles in our reference section).

We also review the experimental literature on attenuating psychological barriers and identify five primary methods that scholars and practitioners have employed for doing so. The landscape of how these methods have been employed suggests that different methods might be more appropriate for different types of barriers. Finally, we discuss the difficulties as well as possibilities of scaling attenuation interventions beyond the samples included in prior experiments.

While future research might seek to identify additional psychological barriers to conflict resolution, our efforts at consolidating the existing literature seem to suggest that scholars have already invested considerable resources in identifying “new” barriers. In many cases, the latest discovery is little more than a rephrasing, reframing, or reconceptualization of previously identified and understood psychological barriers. The marginal benefit of additional research expenditure, this review suggests, might be greater if scholars focus more attention on how different barriers covary, how barriers (or portfolios of barriers) might be attenuated, and how interventions might be scaled in order to resolve or mitigate conflict in organizations, communities, and society.

We are grateful to Professors Francesca Gino and Max Bazerman for comments on earlier drafts of this article. We also thank an anonymous reviewer and attendees of the International Association of Conflict Management conference (July 2019). Finally, we are indebted to Scott Berinato (author of Good Charts: The HBR Guide to Making Smarter, More Persuasive Data Visualizations) for his extensive help with data visualization and the creation of Figure Two.

1. Arguments and positions as extension of self (De Dreu and Van Knippenberg 2005)

2. Automatic activation of conflict‐supporting beliefs (Bar‐Tal 2013)

3. Behavioral guidance (Bar‐Tal 2013)

4. Bias perception (Kennedy and Pronin 2008)

5. Biased assimilation of information (Bar‐Tal 2013)

6. Biased punctuation of conflict (Thompson and Lucas 2014)

7. Cognitive freezing (Kruglanski and Freund 1983)

8. Collective blame (Lickel et al. 2006)

9. Collective emotional orientation (Bar‐Tal and Halperin 2013)

10. Collective fear and angst (Mackie, Devos, and Smith 2000; Halperin, Porat, and Wohl 2013)

11. Collective memory (Paez and Liu 2011)

12. Collective narratives (Auerbach 2010)

13. Competitive victimhood (Noor, Brown, and Prentice 2008)

14. Concession aversion (Kahneman and Tversky 1995)

15. Conflict non‐malleability (Halperin 2016)

16. Conflict uniqueness (Halperin 2016)

17. Conformity (Mitchell 1981)

18. Correspondence bias (Bar‐Tal 2013)

19. Dehumanization (Kteily, Hodson, and Bruneau 2016)

20. Delegitimization (Bar‐Tal 1988)

21. Different political values (Wade‐Benzoni et al. 2001)

22. Dissonance arising from the past (Ross and Ward 1995)

23. Distorted interpretation and organization of information in line with conflict views (Bar‐Tal 2013)

24. Divergent construal (Hastorf and Cantril 1954)

25. Double standard (Oskamp 1965)

26. Egocentric bias (Messick and Sentis 1979)

27. Empathy (Halperin 2016)

28. Ethos of conflict (Bar‐Tal et al. 2012)

29. Exaggerated polarization (Robinson et al. 1995)

30. Group‐based guilt (Doosje et al. 1998)

31. Habituation (Bar‐Tal 2013)

32. Hopelessness and despair (Halperin 2016)

33. In‐group favoritism (Perry et al. 2017)

34. Intergroup anger (Mackie, Devos, and Smith 2000)

35. Group‐based hatred (Halperin 2008)

36. Investments (Bar‐Tal 2013)

37. Loss aversion (Ross and Ward 1995)

38. Memorization of belief‐consistent information and neglect of inconsistent information (Bar‐Tal 2013)

39. Mistrust (Bar‐Tal, Halperin, and Oren 2010)

40. Mobilization of group loyalties (Kelman 2008)

41. Moral amplification (Haidt and Algoe 2004)

42. Moral disengagement (Bandura 1999)

43. Moral entitlement (Bar‐Tal 2013)

44. Naïve realism (Ross and Ward 1995)

45. Negativity bias (Bar‐Tal and Halperin 2013)

46. Non‐differentiation between negative and positive components of opponent’s ideology and symbols of legitimacy (Kelman 1987)

47. Obedience (Milgram 1974)

48. Omission bias (Wade‐Benzoni et al. 2001)

49. Optimistic overconfidence (Bazerman and Neale 1982)

50. Outcasting (Bar‐Tal and Hammack 2012)

51. Out‐group homogeneity (Halperin 2016)

52. Out‐group hostility (Perry et al. 2017)

53. Group entity beliefs (Rydell et al. 2007)

54. Parochial empathy (Cikara, Bruneau, and Saxe 2011)

55. Partisan identity (Wade‐Benzoni et al. 2001)

56. Partisanship (Sherman, Brookfield, and Ortosky 2017)

57. Political labels (Bar‐Tal and Hammack 2012)

58. Prejudice (Allport 1954)

59. Psychological distress (Hirsch‐Hoefler, Canetti,  Rapaport, and Hobfoll 2016)

60. Reactive devaluation (Ross and Stillinger 1991)

61. Resistance to conciliatory measures (Bar‐Tal 2013)

62. Sacred values (Ginges et al. 2007)

63. Schadenfreude (Bruneau and Saxe 2010)

64. Search for belief‐affirming information (Bar‐Tal 2013)

65. Selective attention (Bar‐Tal 2013)

66. Self‐focus (Bar‐Tal 2013)

67. Self‐censorship (Bar‐Tal 2013)

68. Self‐fulfilling prophecy (Merton 1952)

69. Support for aggression (Bar‐Tal 2013)

70. System justification (Jost and Banaji 1994)

71. The certainty effect (Kahneman and Tversky 1995)

72. The illusion of transparency (Thompson and Lucas 2014)

73. Threat perception and cognitive closure (Bar‐Tal 2013)

74. Trait characterization (Bar‐Tal and Hammack 2012)

75. Value‐based self‐enhancement (Wade‐Benzoni et al. 2001)

76. View of conflict as zero sum (Kelman 1987)

77. Fixed‐pie bias (Bazerman and Neale 1983)

78. Risk aversion (Bazerman, Magliozzi, and Neale 1985)

79. Protected values (Baron and Spranca 1997 )

80. Sunk cost (Neale and Bazerman 1991)