Illusions of Autonomy: Why Europe Cannot Provide for Its Security If the United States Pulls Back

In the past decade, Europe's security landscape has changed dramatically. Russia is far stronger militarily than it was ten years ago, and its annexation of Crimea in 2014 and subsequent aggressive actions in Eastern Ukraine demonstrated that territorial revisionism remains a security concern in Europe. The Barack Obama administration's “pivot to Asia,” combined with recurring, sharply critical comments from key policymakers about insufficient European burden sharing —including from Defense Secretaries Robert Gates and Leon Panetta, as well as Obama himself—greatly magnified European concerns about the long-term robustness of the transatlantic alliance.¹ Against this backdrop, in June 2016 the European Union Global Strategy issued a strong call for Europe to achieve “strategic autonomy.”² The momentum behind this call received a boost from the administration of Donald Trump, whose highly critical comments of the North Atlantic Treaty Organization (NATO) reinforced European concerns about the credibility and strength of the U.S. commitment to the Alliance.³ And although President Joseph Biden intends to reinvest in U.S. alliances and in the transatlantic relationship in particular, the polarization of U.S. politics—which now extends to foreign policy—has heightened doubts among European policymakers about the long-term reliability of the U.S. security commitment to the continent.⁴ As President of the European Commission Ursula von der Leyen puts it, “Some shifts in priorities and perceptions run much deeper than one politician or administration” and they do not “disappear because of one election.”⁵ In this regard, the special adviser to European Union (EU) High Representative for Foreign Affairs and Security Policy, Nathalie Tocci, stresses that, irrespective of the U.S. administration, Europeans should therefore not stick their “heads in the sand” and should instead continue to pursue strategic autonomy.⁶

Strategic autonomy can be defined as the institutional capacity to independently plan and conduct military operations across the full spectrum of conflict (including in high-intensity military operations such as expeditionary warfare and territorial defense missions) and to autonomously develop and produce the related defense capabilities with minimal or no assistance from the United States.⁷ Although analysts agree that Europe currently lacks strategic autonomy, recent European defense initiatives—including the European Defense Fund (EDF), the strengthening of the Permanent Structured Cooperation mechanism (or PESCO), the European Intervention Initiative, and the EU Military Planning and Conduct Capability (MPCC)—purportedly indicate that the Europeans are taking meaningful steps toward strategic autonomy, or what some analysts call “the new Grail of European defense.”⁸

The European ambition to seek strategic autonomy amid rising concerns over U.S. commitments to the continent and over Russia's revisionist behavior raises an important counterfactual question: Could Europeans develop an autonomous defense capacity if there were a complete U.S. withdrawal from Europe? Although a U.S. withdrawal from Europe is unlikely in the short term, it is hardly a far-fetched scenario for the longer term. Examining this counterfactual is useful for two key reasons. First, a complete U.S. withdrawal—one entailing an exit from NATO and the withdrawal of all U.S. conventional and nuclear forces from the continent—is the strongest possible incentive that could drive the Europeans to pursue strategic autonomy, and is therefore the best way to assess their capacity to do so. Second, examination of this counterfactual advances the U.S. grand strategy debate in light of the prominent theoretical argument from U.S. “restraint” scholars such as Barry Posen, who argue that a U.S. withdrawal is warranted on the grounds that Europe can quickly and easily create an effective deterrent to Russia.⁹ As we explain, Europe is the key fulcrum in the grand strategy debate between these restraint scholars and “deep engagement” scholars, who favor maintaining current U.S. security commitments in Europe and elsewhere.¹⁰

Determining whether Europeans could achieve strategic autonomy anytime soon if the United States were to pull back from Europe requires an examination of the historical trajectory and the current and likely future state of European interests and defense capacity. Although existing studies have analyzed important elements of each, a more systematic analysis is needed.¹¹ Regarding interests, this article provides the most comprehensive and thorough coding of national threat perceptions across all of Europe, showing where each country falls across a set of defined categories of threat prioritization. Concerning defense capacity, it adds to existing understandings of Europe's deficiency by providing novel longitudinal data on European conventional defense capabilities over the past three decades and by outlining a series of four interwoven challenges that would greatly complicate the pursuit of strategic autonomy.

Our analysis shows that European efforts to achieve strategic autonomy will be hampered by two major constraints: profound defense capacity shortfalls that will be hard to close, and “strategic cacophony,” that is, profound, continent-wide divergences across all the domains of national defense policies, most notably threat perceptions.¹² These mutually reinforcing constraints impose a rigid limit on the capacity of Europeans to achieve strategic autonomy anytime soon. Consequently, if the United States were to fully withdraw, the continent would become significantly more vulnerable to Russian meddling and aggression. Furthermore, if the U.S.-backed NATO were to disappear, this would undermine the only institutional framework that has fostered some degree of coordination in Europe (at the strategic, doctrinal, and capability levels) and partly contained Europe's strategic cacophony. This, in turn, would make institutionalized, intra-European defense cooperation appreciably harder.

Ultimately, we conclude that the notion that Europeans would be able to achieve defense autonomy following a U.S. pullback is illusory.¹³ And if even the major shock of a complete U.S. pullback would be very unlikely to move Europe away from its current strategic cacophony and capability shortfalls, a partial U.S. pullback—a much more likely counterfactual—would be more unlikely to do so. The policy implication is straightforward: if the United States wants European stability, it needs to stay in Europe.

The remainder of the article proceeds as follows. First, we set the stage for our analysis by outlining why the U.S. military presence in Europe, established after World War II, has such significance for the existing U.S. grand strategy debate and what the scenario of a full U.S. pullback from the continent would entail. In the second and third sections, we lay out the overarching constraints that hamper the capacity of Europeans to achieve strategic autonomy. We first shed light on Europe's strategic cacophony, demonstrating that Europeans are divided by contradictory threat prioritizations—and the resulting strategic priorities—regarding Russia, terrorism, and other threats such as regional instability in the Middle East and Northern Africa. We then discuss Europe's profound military capacity deficiency and delineate four major challenges to rectifying it. In the fourth section, we consider the restraint counterargument that, even though Europe is currently split by strategic divisions and hindered by severe capacity shortfalls, a complete U.S. withdrawal would heighten Europeans' threat perceptions of Russia and thus compel the United States and Europe to come together to effectively balance Russia. Building upon our empirical analysis, we argue that there is no basis to support this optimistic assessment in either the conventional or nuclear realm. We conclude with a discussion of the policy implications of our findings for both the United States and Europe.

In his 1796 farewell address, George Washington famously warned: “Europe has a set of primary interests, which to us have none, or a very remote relation. Hence, she must be engaged in frequent controversies the causes of which are essentially foreign to our concerns. Hence, therefore, it must be unwise in us to implicate ourselves, by artificial ties, in the ordinary vicissitudes of her politics, or the ordinary combinations and collisions of her friendships or enmities.”¹⁴ Reflecting this sentiment, from the United States' founding until World War II, detachment from European security affairs was a, if not the, defining element of U.S. security policy.¹⁵

How then did the United States become so enmeshed in Europe's security? After World War II, U.S. officials concluded that, to paraphrase the famous dictum (attributed to Lord Ismay) regarding NATO's purpose, keeping the United States in was the ideal method for keeping the Soviet Union out while keeping Germany down.¹⁶ In other words, a Germany strong enough to check the Soviet Union, absent a major U.S. presence, would have demanded German rearmament and acquisition of nuclear weapons, which would have risked alienating France and other neighbors and wrecking the alliance.¹⁷ Over the four decades of Cold War rivalry, the United States thus built up complex relationships that allowed it to shape the strategic environment in Europe to facilitate balancing Soviet power.¹⁸

After the Soviet Union collapsed in 1991, the United States chose to sustain those relationships by maintaining NATO and its leadership of the Alliance. At the same time, it did drastically cut its forward-deployed troop presence in Europe. In the final phase of the Cold War, approximately 350,000 U.S. troops were based in Europe, a number that plummeted to a mere 118,000 troops in 1995 and was then further reduced almost by half to just around 65,000 active-duty U.S. troops today.¹⁹

Scholars participating in the ongoing U.S. grand strategy debate are sharply divided regarding whether the United States should maintain its military presence in Europe. Stephen Brooks and William Wohlforth—who are proponents of deep engagement—identify seven security benefits that America garners from its security presence in Europe: bolstered regional security in light of a resurgent Russia and strengthened U.S. bargaining leverage with Moscow; a deep and broad institutional framework for coordinating and fostering transatlantic security cooperation; assistance with out-of-area operations; U.S. access to permanent bases, logistical assets, overflight rights, and so on; key infrastructure and lines of communications to sustain U.S.-led military actions in western and central Eurasia, the Middle East, or Africa; U.S. influence and leverage over allies regarding issues such as arms sales to China; and enhanced intelligence cooperation.²⁰ In addition, Brooks and Wohlforth stress that the U.S. security partnership with Europeans helps facilitate cooperation on issues other than security and advance U.S. economic interests.²¹

In contrast, restraint advocates—a large group of more than thirty scholars that includes many of the most prominent members of the security studies field—all agree that the United States' continued membership in NATO and its troop presence in Europe no longer serve U.S. interests and that it is time to fully withdraw.²² Yet, proponents of restraint do not have a uniform perspective concerning the United States' presence in Asia or the Middle East. Regarding the Middle East, some restraint scholars (e.g., Eugene Gholz and Daryl Press) favor the United States completely removing its forces from the region;²³ others (e.g., Stephen Walt, John Mearsheimer, and Barry Posen) advocate that the United States retain a limited onshore military presence in the region.²⁴

The positions of restraint scholars diverge even more dramatically regarding Asia: some (e.g., Christopher Layne, Gholz, and Press) favor quickly ending all U.S. alliances in the region and pulling back all U.S. forces;²⁵ others (e.g., Posen) favor a gradual pullback from the region and argue that “some kind of extended nuclear deterrence relationship will probably remain necessary” in at least some parts of the region;²⁶ and still others (e.g., Mearsheimer and Walt) advocate for a similar stance to deep engagement with a continuation of current alliances and the U.S. military presence in Asia as part of “a major effort” to prevent China from achieving regional hegemony.²⁷ Europe is thus the key fulcrum in the grand strategy debate: all proponents of deep engagement maintain that the United States should stay, whereas all advocates of restraint argue that it should leave.

Restraint scholars support a U.S. pullout by arguing that European states are big enough and rich enough to autonomously address the military threat from Russia (a threat that they claim is the “main security problem for Europe”²⁸). Walt, for example, asserts that the notion that the EU “lacks the wherewithal to defend itself against [Russia] … is risible,” given that “the countries of the European Union are home to more than 500 million people and boast a combined annual GDP [gross domestic product] exceeding $17 trillion,” whereas Russia “has a population of just 144 million and an annual GDP of only $1.6 trillion.”²⁹ For his part, Posen argues that “a coalition of any two of the principal Western European powers—Germany, France, and Britain—could easily balance Russia.”³⁰

For restraint scholars, the core problem is that the United States has provided the Europeans “with such a high level of insurance that they have been able to steadily shrink their militaries and outsource their defense to Washington. … With their high per capita GDPs, these allies can afford to devote more money to their militaries, yet they have no incentive to do so. … This is welfare for the rich.”³¹ According to these scholars, the United States could make better use of these financial resources at home.³²

The counterfactual scenario examined in this article, the one favored by restraint scholars, is that the United States officially exits from NATO and fully withdraws its forces and military units from Europe, including the roughly 65,000 active-duty personnel under the U.S. European Command, 2,000 reservists, 16,350 Department of Defense civilian personnel, and around 930 personnel assigned to NATO's Command Structure. The United States also would no longer continue its rotational presence of air, land, and sea forces throughout Europe as part of the European Deterrence Initiative (which includes a U.S. armored brigade combat team and a combat aviation brigade).³³ In addition, the United States would remove all its European-based nuclear capabilities.

Although it is difficult to envision a full U.S. pullback from Europe in the short term, it is hardly implausible in the longer term in light of both domestic and international dynamics. Structural trends in the international system—most notably, the rise of China relative to the United States and the growing strategic centrality of the Asia-Pacific region—have caused the United States to downgrade the importance of Europe in its grand strategy.³⁴ Moreover, the United States pursued an isolationist grand strategy for most of its history; leaving Europe would simply be a return to its traditional foreign policy baseline regarding the region. And significantly, there is every indication that Trump tapped into, rather than created, the political momentum for curtailing the United States' security presence overseas. Prior to Trump becoming president, U.S. public opinion in favor of the United States disengaging from the world had already increased substantially.³⁵ Reflecting these public attitudes, in the early 2010s, a number of Republican fiscal hawks and liberal Democrats ramped up their calls for eliminating the U.S. presence in Europe.³⁶ Likewise, according to a 2011 poll, 65 percent of the U.S. public favored scaling back U.S. military commitments to reduce the country's debt.³⁷

A U.S. decision to actively withdraw from Europe is not the only means by which this outcome could occur; it could also unfold passively with Europe and the United States drifting further apart over many years, eventually reaching a point where NATO has been hollowed out and exists essentially in name only. In fact, because of rising doubts about the long-term credibility and robustness of the U.S. commitment, many prominent European policymakers and security analysts have concluded that Europe should rely less on the transatlantic partnership and bolster its capacity for autonomous action.³⁸ As then President of the European Commission Jean-Claude Juncker stated in 2016, “If Europe does not take care of its own security, nobody else will do it for us.”³⁹ Yet, as we show in the next two sections, two overarching constraints jointly limit the capacity of Europeans to achieve strategic autonomy: Europe's strategic cacophony and profound capability shortfalls that will take a long time to close.

The first two decades after the dissolution of the Warsaw Pact and the collapse of the Soviet Union constituted an era of strategic exception, characterized by the absence of a major conventional security threat. During this period in which European states lacked any semblance of a unifying threat, wide discrepancies emerged in their national threat assessments. The threat perceptions of European defense policymakers shifted away from conventional state threats to nonconventional ones such as terrorism, instability in the Mediterranean area, migration, the proliferation of weapons of mass destruction (WMD), and failed states.⁴⁰

Russia's invasion and annexation of Crimea in 2014 shattered the long-held assumption that the European territorial status quo would not be upset via the use of military force. Yet, far from bringing Europe together, Russia's assertiveness only further deepened Europeans' profound divergences of threat perceptions, with growing disagreements among Europeans about how to prioritize Russia versus other challenges.⁴¹

Below we provide a bottom-line assessment and systematic coding of national threat perceptions across twenty-nine European countries. We include all countries that are members of the EU or NATO, or both, except for Turkey and seven countries that have GDPs smaller than $25 billion: Albania, Bosnia and Herzegovina, Cyprus, Iceland, Liechtenstein, North Macedonia, and Montenegro. We identify where the threat assessment of each country falls across five categories: (1) Russia is unimportant or not a threat; (2) Russia is a threat, but other threats are more significant; (3) Russia and other threats have roughly equal significance; (4) Russia is the highest threat, but other threats also are significant; and (5) Russia is the dominant threat by far.

To produce these codings, we adopted a nested approach. First, we coded the threat evaluations of these countries made by eighteen experts who contributed to a recent comprehensive examination of European defense policies.⁴² To double-check our codings, we consulted all eighteen authors to ensure that our understanding of each country corresponded with theirs.⁴³ Second, we looked at all available government reports that provide a national assessment of the regional threat environment and prioritize among different threats. In particular, we examined the national security/defense/military strategies, the intelligence threat assessments, the analyses of particular threats (e.g., cyberthreats and terrorism), and regional/geographic analyses of all twenty-nine European states in our study. In total, we examined eighty-seven official documents and reports. (Online appendix A provides a full list of these sources; they are referenced in the footnotes by document number as indicated in this appendix.)⁴⁴

For most states, the combination of these first two sources provided enough information to reliably code national threat assessments. But for others, they were insufficient because official threat assessments were somewhat ambiguous. For these countries, a third step was thus to interview senior foreign policy and defense officials to obtain additional information and gain further clarity into the national threat assessment.⁴⁵ We conclude that Europe is characterized by strategic cacophony (see table 1). Whereas some states rank terrorism and instability in the Mediterranean region at the top of their threat assessments—with little, if any, threat perception vis-à-vis Russia—others identify Russia as their overarching security concern, while largely ignoring the diffuse threats on Europe's southern shores. Between these two extremes, different countries and groups of countries exhibit varying perceptions of their core security challenges. Overall, the continent is marked by profoundly divergent threat assessments and ensuing strategic priorities.

The varied threat perceptions of European states have been shaped by a complex mix of history, politics, and geography, as well as by changes in the regional strategic environment. Details on our country codings are discussed below, according to category of threat prioritization.

Most smaller powers in Western and Southern Europe prioritize as their main sources of concern transnational terrorism, WMD proliferation, and instability across the Middle East and Northern Africa (MENA) and the resulting flows of migrants (see table 1).⁴⁶ By contrast, ever since the collapse of the Soviet Union, which was perceived as the overarching conventional and nuclear threat during the Cold War, Russia has little, if any, significance in their national threat assessments.⁴⁷ Indeed, some of these countries, such as Italy or Spain, have long advocated for sustained engagement with Moscow.⁴⁸

Likewise, two countries that do not share the same level of anxiety held by most Central and Eastern European countries vis-à-vis Russia are Hungary and Bulgaria. Considering the threat of conventional war to be minimal, and given their strong ties with Moscow, they instead prioritize terrorism, migration flows, WMD proliferation, and cyberattacks.⁴⁹

Other countries also prioritize transnational terrorism, regional turmoil around Europe and the MENA, cyberattacks, and illegal migration, but display higher threat perceptions of Russia than do states in the first category (see table 1). They perceive Russia as a threat, but nonetheless see other threats as relatively higher sources of concern.⁵⁰

Croatia's threat assessment, for instance, focuses largely on challenges such as terrorism, regional instability, migration, and the proliferation of WMD.⁵¹ Still, in a veiled yet clear reference to Russia's influence in the Western Balkans, Croatian policymakers put greater emphasis than the first group of countries on threats such as “non-conventional, asymmetric, and cyber actions” that are “planned, permanent and systematic activities supported by state bodies.”⁵²

France is the only major power in this group. Its threat perceptions revolve, foremost, around transnational terrorism and regional instability in Europe's southern periphery. French policymakers consider jihadist terrorism as “the most immediate” threat,⁵³ especially in light of the steep rise in the number of terrorist attacks on French soil since the mid-2010s.⁵⁴ France is also concerned with the proliferation of conventional and WMD-related technology,⁵⁵ as well as with regional instability in Northern Africa and the Middle East.⁵⁶ The French government puts particular emphasis on sub-Saharan Africa, where, partly because of its postcolonial history, France retains “a direct security and economic interest” in the stability of the region.⁵⁷ Accordingly, although France has displayed growing concerns vis-à-vis Russia's assertiveness after the Ukrainian crisis,⁵⁸ other threats remain more significant.

The United Kingdom and Germany—together with less powerful Western European states (Belgium and the Netherlands) and Denmark—consider Russia and other security challenges to be equivalent threats (see table 1).

British policymakers include both Russia and terrorism in the UK's “Tier One“ category of risks (in terms of probability and impact).⁵⁹ In light of Russia's increasingly assertive behavior, they assess that the ”risks from state-based threats have both grown and diversified,“⁶⁰ which is why the UK ”cannot rule out the possibility that [Moscow] may feel tempted to act aggressively against NATO Allies.“⁶¹ According to a UK former senior defense official, the main areas of concerns vis-à-vis Moscow are (1) Russia's military modernization, including the development and deployment of weapon systems that can threaten the UK's NATO allies; (2) Russia's gray-zone activities (e.g., subversion, use of proxies, cyberattacks, use of military-grade nerve agents for targeted killings); and (3) Moscow's activities outside Europe, such as in parts of Africa, but, most notably, in the Middle East.⁶²

Yet, at the same time, the UK sees transnational terrorism as an equally substantial threat. British policymakers have perceived a rising threat from terrorism since at least the 2005 London bombings and the subsequent wave of terrorist attacks that swept across Europe and the UK in the 2010s.⁶³ In their eyes, “ISIL [the Islamic State of Iraq and the Levant], Al Qa'ida, and affiliates remain committed to attacking UK and Western targets” and continue to be “the most direct and immediate threat” to the UK's “domestic security.”⁶⁴ In 2015, the British government therefore decided to increase its counterterrorism spending by 30 percent, including £2 billion of new investment in the capabilities of UK special forces.⁶⁵

Germany, too, considers terrorism and Russia to be threats of roughly equal significance. German policymakers view terrorist attacks as “the most immediate challenge” to their country's domestic security.⁶⁶ In 2018, Germany's minister of interior stated that the security situation concerning terrorism continued to be “very threatening.”⁶⁷ For Germany, transnational terrorism is tied closely to regional stability in the MENA and to the existence of failing states in which terrorist organizations can thrive.⁶⁸ Accordingly, it seeks to bolster cooperation with partners in Africa and the Middle East to train their security forces so as “to create a bulwark against international terrorism.”⁶⁹

At the same time, Germany sees Russia as “openly calling the European peace order into question with its willingness to use force to advance its own interests and to unilaterally redraw borders guaranteed under international law, as it has done in Crimea and Eastern Ukraine.”⁷⁰ According to the ministry of defense, “this has far-reaching implications for security in Europe and thus for the security of Germany.”⁷¹ A comparison of Germany's 2006 White Paper and of the subsequent strategic documents (i.e., the 2011 Defense Policy Guidelines and the 2016 White Paper) highlights the enhanced focus of the German armed forces on territorial defense since the Russia-Georgia war and Moscow's landgrab in Crimea.⁷²

Interviews with current and former German officials reveal that the foreign affairs, interior, and defense ministries have different threat assessments. Whereas the first two consider terrorism to be Germany's main security challenge, the latter prioritizes Russia as the main threat.⁷³ Across the German government, terrorism and Russia ultimately emerge as being roughly equally significant threats.

Smaller Western European powers such as the Netherlands and Belgium similarly consider Russia and other threats to be largely equivalent.⁷⁴ Likewise, in Northern Europe, Danish policymakers rank terrorism and regional instability in the MENA—which can provide fertile ground for terrorists—relatively higher than do their Nordic neighbors in their threat assessments.⁷⁵ At the same time, Russia is seen as posing “a significant security challenge,”⁷⁶ and its military buildup and increased military exercises in the region, as well as its use of gray-zone operations, are considered “a clear challenge” to Denmark.⁷⁷ The Danish government thus sees Russia, terrorism, and regional instability in the MENA as equally significant threats.

Several Northern and Eastern European states have displayed mounting threat perceptions of Russia—which they see as their major threat—especially since the Russo-Georgian War and, increasingly, the Ukrainian crisis (see table 1). Yet, they continue to share security concerns vis-à-vis terrorism, regional instability in the MENA, and illegal migration.

In Northern Europe, Norway and Sweden emphasize both the “long belt of instability” to the south of Europe and terrorism as significant national security concerns.⁷⁸ Yet, most notably since the 2010s, Russia has returned to the top of their national security concerns. In particular, they highlight the development of Russia's anti-access/area-denial (A2/AD) capabilities, its numerous military exercises in Northern Europe, and its activities in the Arctic as amplifying the risk of an accident or a crisis resulting in unintended escalation to war.⁷⁹ The Norwegian government, for example, considers that “Russia's overall military capacity is the most significant security challenge for Norway and NATO.”⁸⁰

Likewise, in Central and Eastern Europe, although the Czech Republic, Romania, and Slovakia also emphasize other security challenges (e.g., instability in the Southern Mediterranean and terrorism), their threat assessments prioritize Russia's assertiveness.⁸¹ While refraining from officially labeling Russia a threat, the Romanian government argues that Russia's naval buildup—and the ensuing “destabilization of the security situation in the Black Sea Extended Region”—“represent the most important factor of military risk against national security.”⁸²

The Baltic states, Finland, and Poland exhibit the highest threat perceptions of Russia in Europe. The former Soviet-controlled states in the Baltic region (i.e., Estonia, Latvia, and Lithuania) prioritize Russia's conventional and gray-zone military threats as their core national security concern.⁸³ Likewise, given Finland's geographical proximity to Russia and their shared border, policymakers in Helsinki have viewed Russia as their dominant national security threat throughout the post–Cold War period.⁸⁴ Finland considers that the “use or threat of military force against Finland cannot be excluded.”⁸⁵

Given its history of recurrent invasion by foreign powers, Poland has also consistently put Russia at the center of its security concerns since the end of the Cold War.⁸⁶ Moscow's “aggressive policy”—through which it aims to “destabilize the internal order of other states and to question their territorial integrity”—is seen as “a threat mainly for Poland and other countries in the region.”⁸⁷

European national assessments thus diverge profoundly regarding the prioritization among different threats. Significantly, Europe's strategic cacophony greatly exacerbates a second overarching constraint on Europe achieving strategic autonomy: severe military capacity gaps that cannot be closed anytime soon.

Since the end of the Cold War, Europe's defense capacity has markedly decreased.⁸⁸ Operationally, the 2011 European military action in Libya revealed a severe shortage of key enablers for offensive military operations: the United States had to provide critical capabilities that the Europeans otherwise lacked, such as air-to-air refueling; suppression of enemy air defenses; and intelligence, target acquisition, and reconnaissance.⁸⁹ Indeed, a recent systematic study by the International Institute for Strategic Studies (IISS) and the German Council on Foreign Relations found that, because their capability shortfalls are so significant, Europeans would struggle to autonomously undertake operations even at the low end of the spectrum of conflict (such as peace enforcement missions).⁹⁰

In this section, we focus on Europeans' capacity for conventional warfare because it is indispensable for defense and deterrence vis-à-vis Russia and because this allows us to directly address the argument of restraint scholars who maintain that the Europeans could autonomously balance Russia with ease. We identify four major challenges that are likely to hinder the capacity of Europeans to develop an autonomous conventional defense capacity.

During the Cold War, Europeans invested heavily in the kind of conventional capabilities required for conventional deterrence and defense. But after the Cold War, European defense spending plummeted, and a great proportion of these limited resources were directed toward out-of-area operations.⁹¹ As a result, Europeans are lacking in even the most basic conventional deterrence and defense capabilities. A key reason for this situation is Europe's strategic cacophony. The five economically largest European countries—the UK, France, Germany, Spain, and Italy—are all located in Western or Southern Europe, which collectively have greatly de-emphasized the territorial defense mission since the end of the Cold War. In contrast, states in Central and Northern Europe have tended to focus relatively more on territorial defense, especially after Russia's 2014 invasion of Crimea; yet, these parts of Europe contain only small to medium-sized countries.⁹²

Until now, there has been no long-term examination of the year-to-year shift across all of Europe of the kinds of core capabilities needed for conventional deterrence and defense. To address this gap, we systematically gathered data from the IISS Military Balance for the 1990–2020 period on three core military systems for conventional warfare: main battle tanks (MBTs), armored personnel carriers (APCs), and artillery. To be sure, conventional warfare requires more than simply land capabilities. Yet, Russia's A2/AD capacity is aimed at eroding, or nullifying, NATO's local control of its airspace, thus compelling NATO forces, in the case of conflict, to operate in an environment of land warfare with contested air support.⁹³ In this context, land resistance—and thus land capabilities—become key, which is why we focus on these three specific systems (they constitute a sample of the needed land warfare capabilities). The data for MBTs of Europe's major powers are displayed in figure 1.⁹⁴ (Online appendix C shows the data on MBTs of medium and smaller European countries as well as the data for APCs and artillery for all European countries.)

These data underscore the marked decline of European conventional warfare capabilities in the past three decades. From 1990 to 2020, the combined European total number of MBTs plunged by 85 percent; APCs fell by 64 percent; and artillery declined by 56 percent. As Sven Biscop concludes, “Europe's capability shortfalls are such that it can neither meet its NATO obligations for territorial defense, nor achieve strategic autonomy with regard to the protection of Europe.”⁹⁵

In reality, the situation is even worse than these data indicate, because most European militaries have significant readiness deficiencies. For example, an analysis by the German Parliamentary Commissioner for the Armed Forces concluded in 2018 that the “readiness of the Bundeswehr's major weapons systems is dramatically low in many areas,”⁹⁶ noting that only 39 percent of Germany's Leopard 2 battle tanks were available for use given a lack of spare parts; the operability of only a quarter of its PUMA infantry combat vehicles; the nonavailability of any of its six submarines; and the ability of less than half of its Eurofighters and Tornado combat aircraft to fly.⁹⁷ Significantly, Europe's readiness problems, such as the obsolescence of its MBTs, are projected to become even more challenging in the decades ahead.⁹⁸

As dramatic as these weapons shortfalls are, European defense spending—if allocated properly—could eventually secure the needed systems. Yet, not only is the efficient allocation of resources a major challenge because of Europe's strategic cacophony (as detailed below), but securing the needed weapons systems would only be the first step.

The effective employment of modern weapons systems is far more challenging than in past eras for a variety of reasons. A key consideration is the immense premium put on command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR). C4ISR—often referred to as the “nervous system” of modern militaries—is crucial for gathering information about the combatants, for effectively processing that information, and for disseminating and using that information to develop and implement complex plans.⁹⁹ NATO's 2011 mission in Libya shows the heavy reliance of Europeans on the United States' C4ISR capacity. Europeans would therefore need to develop their own C4ISR capacity to be able to autonomously balance Russia, which would not be an easy undertaking given that Russia is no Libya. They would need large amounts of new C4ISR systems (e.g., reconnaissance and communication satellites; early warning and control aircraft; sensor systems; air, naval, and land command and control platforms), the most complex of which have very long development times. Notably, the already significant difficulty of Europeans assembling the needed systems would be made even more acute if the UK's exit from the EU ends up meaning that British capabilities also need to be replaced: at present, the UK detains, among other capabilities, 53 percent of the EU's combat intelligence, surveillance and reconnaissance heavy unmanned aerial vehicles (CISR UAVs), 42 percent of airborne early warning and control aircraft, and 38 percent of electronic-intelligence aircraft.¹⁰⁰

In addition, European countries lack the kind of specialized personnel needed to operate modern weapons systems effectively. Redressing this weakness would be a significant undertaking, as they have reduced their number of military personnel drastically since the end of the Cold War. As figure 2 shows, the size of the total active militaries of the large European powers declined by 57 percent during the 1990–2020 period.¹⁰¹ Furthermore, beyond the difficulty of securing the financial resources to pay the needed personnel, recruiting sufficient specialized personnel would be a major challenge, as demonstrated by the difficulties faced by many European militaries in attracting personnel for skilled positions.¹⁰² Notably, a recent study has shown that the employment of advanced weaponry calls for highly skilled and highly trained military personnel, which are now more difficult to recruit and retain in the military.¹⁰³ Obtaining specialized military personnel to operate modern weaponry is only the beginning; they must also be trained to effectively use modern weapons, which is extremely challenging and time consuming, partially because these weapons need to be used as part of a cohesive package that places a premium not just on information gathering, but also on coordination and delegation.¹⁰⁴ It has taken U.S. military personnel an extraordinarily long time to develop the skills required for effectively using today's weapons systems: as Posen stresses, the United States' “development of new weapons and tactics depends on decades of expensively accumulated technological and tactical experience.“¹⁰⁵ It would likely take Europeans even longer to develop the needed skills, given differences across countries regarding operational cultures, levels of ambition, languages, and so on.¹⁰⁶

Finally, the effective use of modern weaponry in the European theater depends on European forces being able to move quickly and securely over large distances within Europe. Yet, as a UK parliamentary report puts it, “NATO has difficulty moving large forces” across Europe.¹⁰⁷ In recent years, the Europeans have sought to bolster military mobility through a variety of initiatives dispersed across different institutions (within both the EU and NATO).¹⁰⁸ Yet, the movement and training of military personnel and assets in Europe remain severely hampered by a combination of capability shortfalls, legal/procedural hurdles, and infrastructural deficiencies that will not be easy to resolve.¹⁰⁹

An additional challenge is institutional. Europe's strategic cacophony has prevented Europeans from developing an autonomous, military-planning, command and control (C2) structure.¹¹⁰ Indeed, a report by the European Parliamentary Research Service explains that one of the greatest challenges of European defense is “the lack of integration of the military structures of the Member States.”¹¹¹ Although an effective and autonomous European defense would require the creation of a permanent planning and C2 infrastructure, the question of developing an autonomous Operational Headquarters (OHQ) has proven highly divisive.¹¹² An OHQ was never established because of conflicting national interests and priorities among Europeans, in particular France, Germany and the UK. Whereas Paris has long supported the establishment of a military OHQ to bolster the EU's strategic and operational planning structures and its contingency planning and C2 capacity, London has strongly resisted, seeing it as a duplication of NATO's assets. Germany has stood somewhat in between, though closer to the UK, favoring a focus on civilian-military planning and C2, not least to avoid duplicating structures already existing at NATO.¹¹³ As a result, the EU remains entirely dependent on NATO or national assets for the planning and conduct of major executive operations, for which it has no autonomous military structures.¹¹⁴

If the United States were to pull back from Europe, it remains to be seen whether the Europeans could rely on a “Europeanized” NATO, in which the integrated structures would stay in place but without the United States.¹¹⁵ Military planning and C2 require a clear chain of command. When NATO was created, Europeans agreed to be under U.S. military command, rather than attempting the far more difficult task of agreeing to be under the command of another European country or group of European states. More generally, as the hegemonic power in NATO, the United States has facilitated institutionalized cooperation among Europeans and helped partly contain Europe's strategic cacophony.¹¹⁶ For decades, a U.S.-led NATO has been the overarching shaper of national defense policies and military transformation in Europe, helping overcome coordination and collective-action problems.¹¹⁷ In light of Europe's deep-seated strategic divisions, a U.S. disengagement would amplify these coordination and collective action problems (assuming NATO survived) and would further hinder institutionalized, intra-European defense cooperation at all levels: strategies and doctrines; training; operational learning; interoperability; and joint capability development. Likewise, without the United States, the persistent and profound divergence of threat perceptions and strategic priorities among Europeans is likely to impede their capacity to agree on shared C2 structures for conducting operations, except for the lowest end of the spectrum of conflict (e.g., peace support operations).¹¹⁸

As a result of strategic cacophony, the EU has, in fact, struggled mightily to create even the most minimal C2 structure. As Luis Simón underscores, “It has taken nearly 20 years of allegedly significant steps for the European Union to establish a ‘Military Planning and Conduct Capability’ composed of up to 25 staffers, devoted to assisting with the planning and conduct of so-called non-executive (i.e., training and assistance) missions,” with an advisory role only.¹¹⁹ Ultimately, given Europe's deep-seated divergences, there is no basis for optimism that Europeans will be able to agree being under the permanent command of another European country for deterrence and defense or to consistently undertake effective institutionalized military cooperation without the enabling role played by the United States within NATO.

If Europeans want to be strategically autonomous, they will have to produce the defense systems they need without being reliant on the United States. The entrenched fragmentation of Europe' defense industrial base, however, would make this a daunting task.

On the demand side, European states have consistently privileged domestically procured defense equipment over European arms cooperation. According to data from the European Defense Agency, from 2006 to 2015, collaborative defense procurement in Europe accounted for less than one quarter of total procurement.¹²⁰ For example, a mere 7 percent of the European surface vessels currently in use have been built through European armament cooperation.¹²¹ As for fighter aircraft—where the economic incentives for European-wide collaboration are especially powerful given the immense cost and complexity of these systems—there has been relatively limited defense cooperation: less than a third (32.6 percent) of combat aircraft used by EU militaries come from European collaborative production.¹²² Similarly, European states spend more than 80 percent of their military research-and-development budgets within national borders.¹²³

On the supply side, these compartmentalized national markets for weapons systems have resulted in a fragmented and noncompetitive European defense and technological industrial base (EDTIB) characterized by duplication, inefficiencies, endemic overcapacity, and a lack of economies of scale.¹²⁴ In 2017, 178 different weapons systems were in use in the EU, compared to 30 in the United States.¹²⁵ As a result, the components that sustain the industrial capacity to deliver high-end to low-end capabilities are scattered across Europe.¹²⁶ This is a significant problem given that today's scale requirements are massive for many weapons systems, which also explains why Europe remains highly dependent on the import of key components and weapons systems from the United States.¹²⁷

Europe has recognized the need for stronger defense production coordination for a long time, and the mechanisms for fostering European-wide collaboration in weapons production have been a topic of discussion for the past several decades. On the demand side, this coordination would require a uniform European procurement policy, with common requirements and with defense industrial cooperation among EU countries being prioritized over national procurement.¹²⁸ And on the supply side, this would require an integrated defense and technological industrial base (e.g., with one or two major European prime contractors per sector) capable of sustaining military innovation and the development, production, and maintenance of arms at reasonable cost.

Yet, efforts to formulate the kinds of policies that would foster European-wide defense collaboration have been feeble. As Matthew Uttley explains, initiatives taken over the years to rationalize and bolster the EDTIB have had a “limited impact,” because governments see a strong national DTIB as a necessary prerequisite for national political sovereignty and, as a result, “national protectionist practices” remain “the dominant driving force in E.U. defense procurement.”¹²⁹ A report by the European Parliament confirms that a key reason for this lack of collaboration is Europe's strategic cacophony, specifically, “the current fragmentation of the defense market in terms of demand, regulations, standards and supply.”¹³⁰

Together, Europe's strategic cacophony and its defense capacity shortfalls feed and reinforce each other. For one thing, many of the needed steps to make up for Europe's defense capacity shortfalls will require prolonged cooperation; Europeans would thus need to overcome their entrenched strategic cacophony not just for a short time, but over a very long period. Moreover, because diverging interests hamper defense industrial cooperation among Europeans, this—coupled with major capability shortfalls—deepens their technological dependency on the United States, further reinforcing the challenges to addressing Europe's capability shortfalls.

Restraint scholars arguing for a U.S. pullout would undoubtedly respond that, even if Europe is currently split by strategic divisions and has severe defense capacity shortfalls, a U.S. withdrawal would result in heightened European threat perceptions of Russia and thereby lead Europeans to bolster their defense investments—thus prompting them to come together to balance Russia (through a balancing coalition or through the EU, or both). For restraint scholars, it is the U.S. presence in Europe that affords Europeans the luxury of low threat perceptions of Russia and thereby drives them to underinvest in defense. Below, we assess the validity and robustness of this counterargument.

We now evaluate how European threat perceptions would likely evolve if the United States were to pull back, focusing first on Europe's three major powers (France, the UK, and Germany) and then on its medium and lesser powers.

Given its geographical location, colonial past, and continued engagement in Africa, France tends to look south rather than east for the defense of its core strategic interests.¹³¹ Furthermore, France's strategic outlook remains shaped partly by its Cold War, Gaullist foreign policy legacy, which was based on the willingness to carve out a “third way” between the Soviet-led and the U.S.-led blocs through some form of accommodation with Moscow while maintaining an independent nuclear force and a French area of influence in Africa.¹³²

The UK, as an offshore seapower, has since the early Cold War concluded that the only way to deter the Soviet Union (and later Russia) is to use the United States as a counterweight.¹³³ Accordingly, the “special relationship” with the United States, both bilaterally and through NATO, has been the center of gravity of the UK's defense policy—as illustrated by its heavy reliance on U.S. military technology.¹³⁴ Indeed, NATO has been the main vehicle through which Britain has sought to entrench U.S. power in Europe and deter external threats.¹³⁵

Likewise, Germany, because of its history and location in the heart of the European continent, has strategic priorities different from those of France. The defeat and subsequent occupation of Germany in World War II, including by the Soviet Union, was followed by the division of the country in two, with one side under Soviet influence—thus making Germany the geostrategic epicenter of the Cold War. After its reunification and the end of the Cold War, as well as its self-imposed stringent parliamentary constraints on the use of military force, Germany has opted for a combination of economic and political integration with the EU and military reliance on NATO, with the United States as the ultimate guarantor for its security and the stability of the continent.¹³⁶

Idiosyncratic historical legacies, geography, and distinctive local security environments have thus profoundly shaped the threat assessments of the three major European powers. To be sure, these differences existed during the Cold War, too, but they were muted by the overwhelming, common Soviet threat.¹³⁷ By contrast, in light of the diversification of the post–Cold War threat environment, if the United States withdrew from the continent, the threat perceptions of these major powers would be unlikely to converge around Russia.¹³⁸

In such a scenario, the UK and Germany would be prone to exhibit heightened threat perceptions vis-à-vis Russia. Given their historical reliance upon NATO as their ultimate security guarantee, if the United States were to remove its conventional and nuclear forces, the credibility of NATO's deterrent vis-à-vis Russia would founder in the eyes of British and German policymakers. As a result, there is every reason to expect they would raise the significance of Russia and of territorial defense in their defense planning. At the same time, they would still have to reckon with other significant threats (e.g., transnational terrorism and regional stability in the MENA).

By contrast, France's threat assessment would most likely remain unchanged if the United States withdrew. Although France might view Russia with greater concern, it would continue to prioritize terrorism and, crucially, threats on Europe's southern periphery (i.e., regional instability in the greater Mediterranean area, in general, and in Africa, in particular). As a senior current French defense official put it in an interview, “If the United States withdrew, the risk represented by Russia would ostensibly be greater but, at the same time, it would be greater only if France considered that the threat posed by Russia to the Baltic states, Poland, etc. constitutes a threat to our vital interests, which is far from sure.” This is because threats to Europe's southern periphery, such as “the destabilization of Africa or the Middle East are considered to be a much higher priority than Russia. … Our vital interests are not threatened by Russia.”¹³⁹

In sum, in the case of a complete U.S. pullback from the continent, London and Berlin would likely move rightward into the second column from the right in table 1 (Russia is a higher threat, but other threats are also significant), while France would not shift from its current position. Given their differing threat prioritizations, the United Kingdom, Germany, and France would be very unlikely to reach agreement on a common position vis-à-vis Russia. Germany and the UK might lean more toward balancing and expand bilateral defense cooperation to that end. However, unlike countries that view Russia as the dominant threat by far (i.e., the Baltic states and Poland), they would face important trade-offs in their allocation of resources—between territorial defense and power projection capabilities, between Europe's eastern and southern periphery, and so on—given that they would continue to grapple with other significant threats. For its part, because France would likely continue to prioritize threats on Europe's southern periphery, it would be unlikely to provide a substantial (if any) contribution to a balancing coalition. In fact, it might opt for accommodation with Russia to develop a sphere of influence in Western/Southern Europe or, potentially, even see some strategic advantages to band-wagoning with Russia.

This predicament would be further compounded by fundamental divergences in threat perceptions among Europe's medium and small powers. Except for lesser powers in Northern and Eastern Europe (i.e., the Baltic states and Poland), which would consistently see Russia as their overriding threat, the other medium and small European states would likely display profoundly different reactions to a U.S. pullback, depending on their geographic location, history, and strategic priorities. While some countries would undoubtedly perceive a higher threat from Russia and thus revise their threat assessments (moving one column to the right in table 1), others would likely maintain their existing threat hierarchization given the equivalent or higher priority they assign to other threats or regions, or both. In fact, there is every indication that most medium and small European countries that currently perceive threats other than Russia to be more significant or dominant would be highly unlikely to revise their threat assessment. Several of these countries might even become neutral or bandwagon with Moscow. It is therefore extremely implausible that all European states would move Russia up in their ranking of threats. And even if they did, the cacophony of threat perception would remain, with only a few lesser powers in Northern and Eastern Europe perceiving Russia as their dominant threat.

Restraint scholars might reply that the above discussion is excessively pessimistic about the chances for European defense coordination because it neglects the role the EU can play in bringing Europe together in the security realm if the United States leaves.¹⁴⁰ The EU is not an effective institutional platform for overcoming Europe's strategic divergence, however. There are many reasons for this, with the most notable being that the EU is a kaleidoscope of countries with diverging interests that operates on the basis of consensus in the field of foreign and defense policy—thus making the Common Security and Defense Policy a “structurally limited undertaking.”¹⁴¹ If the United States were to pull back, rather than work to overcome European divisions, the EU would be prone to inaction because of such divisions. Thus, only an effective institutional structure could probably overcome, or at least mitigate, Europe's divisions, but strategic cacophony would prevent the EU from being enabled to perform this function.

A complete U.S. withdrawal would thus not mitigate Europe's strategic cacophony and could exacerbate it. Restraint scholars might argue, however, that, even if threat perceptions did not converge across Europe, balancing Russia would not require much effort because it is so weak. Yet, Russia is a much tougher adversary to match than restraint scholars now assess it to be—both in the conventional and the nuclear realms.

conventional defense and deterrence. As Michael Kofman and Richard Connolly convincingly argue, “Russian military expenditure is considerably higher” than commonly estimated.¹⁴² Of key importance, they stress, is that Russia gets a lot for what it spends on its military: it pays its soldiers a pittance in rubles, and, even more important, it buys its weapons from its own defense contractors in rubles, not dollars. Moreover, the Russian government has squeezed profits in the defense sector, making the weapons it buys artificially cheap. Notably, Russia's unusually high capacity to produce advanced weaponry using domestic resources is a legacy of the Soviet Union's massive level of defense production during the Cold War. Ultimately, Kofman and Connolly maintain that, because Russia's rubles can purchase so much military power so cheaply, it is inappropriate to use market exchange-based estimates of its military spending. Based upon purchasing power parity exchange rates, “Russia's effective military expenditure actually ranged between $150 billion and $180 billion annually” (from 2015 to 2019), and “taking into account hidden or obfuscated military expenditure, Russia may well come in at around $200 billion.”¹⁴³ Given this understanding, Russian military spending likely exceeds the combined levels of defense expenditures of the three major European powers (France, Germany, and the UK).

High levels of military spending have, in turn, spurred significant modernization and expansion of Russia's military forces, particularly in the 2010s.¹⁴⁴ The Russian Federation is the descendent state of the Soviet Union, which created a formidable military industrial base with a huge cadre of highly trained personnel, providing a strong foundation for Russia's current military infrastructure. Although the Russian armed forces still display important weaknesses in areas such as surface shipbuilding, in the past decade Moscow has substantially “modernized its armed forces through a massive introduction of new and modernized weapons and infrastructure, accompanied by radical structural changes in the military organization, evolving modes of operation and a sharply increased number, scale and complexity of military training and exercise.”¹⁴⁵ Of particular note, from 2015 to 2019, Russia's army increased in size by almost 25 percent.¹⁴⁶ (In online appendix D, we measure the military capabilities of Russia and four potential European balancing coalitions regarding two overall indicators of military personnel [total active and total reserves] and three core weapon systems for conventional warfare [main battle tanks, artillery, and armored personnel carriers]. Across all five of these measures, the data show that Russia possesses a very substantial military superiority as compared to all four potential European balancing coalitions.)

Additionally, Russia possesses substantial C4ISR capabilities for employing weapons systems in a coordinated manner and for managing military operations. These capabilities are the combined result of legacy Soviet systems and of the Kremlin's ongoing military modernization effort.¹⁴⁷ Especially in the past decade, Russia has developed a more modular, flexible force structure with an emphasis on joint forces through a large-scale military modernization.¹⁴⁸

Military satellites are a useful indicator for understanding why Europeans would have difficulty building up the necessary C4ISR infrastructure for balancing Russia. For one, military satellites are critical, because they enable the rest of the C4ISR architecture to operate effectively by facilitating the flow of informational inputs. Specifically, military satellites are crucial for communications, navigation, early warning, attack assessment, and surveillance and reconnaissance—and thus are key for pooling and employing military power. Other C4ISR systems, such as ISR UAVs and airborne early warning and control systems constitute more specific components of a C4ISR architecture that play particular roles therein. Furthermore, whereas full comparison data are available for military satellites, existing databases do not list other C4ISR capabilities systematically. The profound gap between Russia and European countries in military satellites is shown in table 2.

To be sure, notwithstanding such quantitative preponderance in military satellites, one challenge faced by the Russian military in past decades has been the integration of highly interoperable systems for network-centric warfare.¹⁴⁹ Yet, Russia has placed such systems (referred to as the Reconnaissance Strike Complex in Russian strategic parlance) at the “epicenter” of its military modernization in the 2010s, investing massively in C4ISR integration and electronic warfare and in modernizing infrastructure, while boosting and streamlining command and control, among other features.¹⁵⁰

The net result is that, as stressed by a 2019 RAND report, the Kremlin has implemented “a modern, whole-of-government C4ISR infrastructure that will enable Russia to pursue its vision of net-centric or ‘non-contact warfare’”; these “advances in long-range strike, Russia's command and control and information gathering systems are fundamental in their ability to compete directly with the West and dominate regional adversaries”¹⁵¹—an assessment shared by other studies.¹⁵² Significantly, the Russian military tried and tested its C4ISR capabilities during the Syrian conflict.¹⁵³

The experience of European states during the 2011 Libyan conflict showed that they lack the technological infrastructure and personnel to autonomously use weapons systems in a coordinated manner: they would need to replace the United States' C4ISR systems that they currently rely on; hire and train the personnel to operate them; and develop a permanent, effective command structure to conduct effective joint military operations in wartime. Likewise, in stark contrast to Russia's unity of command, Europeans display an “enormous variation” in their C4ISR capacities, with “both technological and operational gaps within Europe.”¹⁵⁴ In sum, Europe exhibits a cacophony of C4ISR capabilities.

A final and related consideration that restraint scholars do not sufficiently recognize is that Russia gains efficiencies—when compared to Europe—because it is a single actor, rather than a collective patchwork of countries. By contrast, as a 2018 European Parliament report concludes, “It is precisely because European defense is fragmented by the decisions of 27 political and military chiefs of staff, duplicates the same research, the same programs and the same capabilities and has no chain of command that it is, collectively, inefficient.”¹⁵⁵ The report notes further that “increasing the level of spending without first addressing the coherence between the different national defense systems would only increase the amount of wastage.”¹⁵⁶ Exactly how much efficiency is lost would depend on how many European countries would need to act together to balance Russia; but even two actors working together would result in less efficacy and effectiveness as compared to a single, unitary actor of comparable size.¹⁵⁷ If the United States pulled back, a single, centralized Russian actor would confront a group of potential European balancers with diverging threat perceptions that would face coordination challenges likely to hamper their capacity to devise a common strategy, to share the burdens of their defense investments, to rationalize Europe's highly fragmented defense industrial base, to build integrated C2 structures, and to sustain the development and deployment of a C4ISR capacity. As a report of the French Senate states, “Compared to other European countries, Russia enjoys a considerable but not quantifiable advantage: unity of command. The Russian army has one commanding authority, one hierarchy, one language, and one equipment range. Obviously, at the operational level, these are very important assets.”¹⁵⁸

nuclear deterrence. As a legacy of the Cold War, Russia maintains a formidable arsenal of approximately 6,400 nuclear weapons, which vastly overshadows the combined arsenals of France and the UK (290 and 195 nuclear weapons, respectively).¹⁵⁹ In addition to Russia's numerical preponderance, it matters greatly that this force is wielded by a single actor, not a collective one. In contrast, strategic divergences and technological constraints are highly likely to hamper the emergence of a European nuclear deterrent either through the Europeanization of the French and/or British nuclear deterrents and/or through a German nuclear deterrent.

As Ulrich Kühn and Tristan Volpe explain, Germany would have to surmount major technical, political, and security obstacles before acquiring a nuclear deterrent.¹⁶⁰ Not only would it face the domestic and international pressures fueled by reviving fears of German hegemony, but it would have “to either repurpose its nuclear energy infrastructure for weapons production or sprint to the bomb from new military facilities,”¹⁶¹ a prospect made even more unlikely given that Germany plans to shut down its entire nuclear fleet by 2022.¹⁶² Accordingly, “Germany does not have the required wherewithal for even a rudimentary program.”¹⁶³

In turn, the Europeanization of nuclear sharing (or Euro-deterrent) based on the nuclear capabilities of France and/or the United Kingdom independent of the United States would also “face high hurdles and immense costs that might well prove prohibitive.”¹⁶⁴ French nuclear experts note that there is “near-zero appetite in France for transferring its nuclear assets to Europe.”¹⁶⁵ Likewise, Barbara Kunz observes that analysts across Europe agree that the Europeanization of the French bomb, however defined, is “unlikely and hardly feasible.”¹⁶⁶

The prospects of a Franco-British nuclear deterrent are even less likely. For one, it is highly improbable that French or British policymakers would be willing to sacrifice London or Paris for Tallinn or Riga. Second, the UK has left the EU, so France and the UK would have to overcome their previously discussed divergent strategic priorities to create an integrated Franco-British military structure for nuclear planning outside the EU. Finally, the heavy dependence of the UK's nuclear deterrent on U.S. technology and on cooperation with the United States would further complicate such an endeavor.

Ultimately, the notion forwarded by restraint scholars that European countries can easily and quickly balance Russia is ungrounded. Balancing Russia would be extremely difficult, and such a buildup would necessarily take a very long time. Our interviews with European policymakers reveal that they clearly understand this problem. A former UK ministry of defense official stresses that the “temporal factor would be quite long. … These sort of capabilities take a long time to develop.”¹⁶⁷ Likewise, as a former German official bluntly explains, “The whole defense and capability requirements would be so extreme that the upgrade that would be needed to fill the gap if the U.S. completely withdrew is totally off limits for the foreseeable future.”¹⁶⁸

Europe is characterized by profound, continent-wide divergences across national defense policies, particularly threat perceptions, as well as by a fundamental defense capacity shortfall that cannot be closed anytime soon because of a series of overlapping challenges. Given the combination of strategic cacophony and capacity gaps, which are mutually reinforcing, Europeans are currently not in a position to autonomously mount a credible deterrent and defense against Russia. This situation would likely continue for a very long time, even if there were a complete U.S. withdrawal from the continent, and all the more so in the event of a partial U.S. withdrawal, a much more likely counterfactual. If a U.S. pullback were to occur, it would leave Europe increasingly vulnerable to Russian aggression and meddling, allowing Russia to exploit Europe's centrifugal dynamics to augment its influence. A U.S. withdrawal would also likely make institutionalized intra-European defense cooperation appreciably harder. Accordingly, a U.S. pullback would have grave consequences for peace and stability on the continent.

These findings have major implications for both sides of the Atlantic. In Europe, scholars and policymakers need to be realistic. The strong desire for strategic autonomy is justified and understandable, but it is necessary to discern between distant hopes and present realities. Ultimately, the barriers to strategic autonomy are so substantial that the achievement of this goal would require a long-term, sustained and coordinated effort. Sound European defense policymaking needs to reflect this: working under an unrealistic assumption that Europeans can quickly achieve strategic autonomy is both unwarranted and unwise. Pursuing unrealistic goals can, in fact, undermine the achievement of realistic ones. Instead, European policymakers should focus on a manageable, affordable set of initiatives for augmenting military capacity in the short term that the United States would see as valuable—and thus would help consolidate the transatlantic alliance—but that would nevertheless also prove useful if the United States does someday pull back. Such an approach could gradually and cumulatively create the foundations for greater commonality and cooperation in the future and, over time, help mitigate the centrifugal dynamics at play in Europe.

In the United States, restraint scholars—virtually all of whom are self-described realists—also need to be realistic. Far from portraying the world as it is, their assessment of Europe is guided by an unfounded optimism that Europeans can easily balance Russia if the United States pulled out. Currently, Europe is presented by restraint scholars as the “easy” case for a U.S. withdrawal, with Asia being the “hard” case.¹⁶⁹ Although China is rising fast and already has much more latent power than Russia, the latter is a greater threat to the United States' European allies than the former based on the other three components of the balance of threat: geographic location, offensive military capabilities, and aggressive intentions.¹⁷⁰ The assessment of restraint scholars that pulling back from Europe is an easy call ultimately rests on a wholly unsubstantiated assumption: that an effective European balancing coalition would emerge quickly if the United States pulled back. What our analysis shows is that Europeans would for a very long time be unable to effectively confront Russia on their own if the United States were to withdraw, and thus if America does want stability in Europe, it should retain a presence on the continent.

To be clear, this analysis does not mean that the United States should never pull back from Europe: in an ideal world, Europeans would and should develop the institutional and material capacity to defend themselves without needing to rely on the United States. But until Europeans can come together effectively in the political and foreign policy realms—a process that will take a very long time to emerge—it is important to be realistic and recognize that a U.S. departure would be destabilizing.

For constructive feedback, the authors would like to thank Jan Joel Andersson, Jonata Anicetti, Christian Anrig, Félix Arteaga, Jordan Baev, Jordan Becker, Lucie Béraud-Sudreau, Bruno Cardoso Reis, Dionysios Chourchoulis, Fabrizio Coticchia, Eugenio Cusumano, Julien Demotes-Mainard, Darrel Driver, Filip Ejdus, Daniel Fiott, Giuliano Fragnito, Andrew Futter, Bastian Giegerich, Andrea Gilli, Mauro Gilli, Clément Godbarge, Gunther Hauser, Keith Hayward, Dorle Hellmuth, Ben Hodges, Stephanie Hoffman, Adrian Hyde-Price, Andres Kasekamp, Benjamin Kienzle, Wim Klinkert, Ina Kraft, Ulrich Kühn, Alexander Lanoszka, Arthur Laudrain, Douglas Lute, Alexander Mattelaer, Mauro Mantovani, Yohann Michel, Andrew Michta, Francesco Moro, Michal Onderco, Frédéric Pesme, Magnus Petersson, Barry Posen, Peter Roberts, Sten Rynning, Olivier Schmitt, Luis Simón, Ian Speller, James Sperling, Thierry Tardy, Matthew Uttley, Mark Webber, Moritz Weiss, William Wohlforth, Marco Wyss, Katarzyna Zysk, the anonymous reviewers, and anonymized European foreign and defense policy officials. The authors also are grateful to Rohan Chakravarty and Tyler Vergho for their outstanding research assistance.