NATO Expansion in Eastern Europe: Strategic Trajectories Beyond 2025

Executive Summary

The future of NATO expansion in Eastern Europe beyond 2025 represents one of the most consequential security questions facing the transatlantic alliance. As of 2026, there are 32 NATO countries, with Finland joining in April 2023 and Sweden in March 2024. However, further enlargement into the post-Soviet space faces unprecedented obstacles. NATO says Ukraine 'will become a member' of the Alliance, but has not set a timeframe, while Georgia's NATO aspirations have stalled amid political turmoil and Moldova maintains constitutional neutrality despite growing security cooperation.

This strategic assessment examines three interconnected dynamics reshaping NATO's eastern frontier. First, the institutional mechanisms for enlargement have evolved substantially, with Allies deciding at the 2023 Vilnius Summit that Ukraine's path to full Euro-Atlantic integration has moved beyond the need for the Membership Action Plan. Second, defense spending across Eastern European NATO members has surged dramatically, with Poland, Estonia, Latvia, and Lithuania demonstrating notably high commitments, each allocating around 3 to 4 percent or more of GDP to defence, reflecting heightened geopolitical risks in Eastern Europe. Third, Russian military reconstitution threatens to compress the timeline for future confrontations, as Russia increased its army personnel by 234,000 in 2025, assembled a new army corps and motorised rifle division near Estonia in 2024, and formed 5 new divisions, 13 brigades, and 30 regiments in 2025.

The prospects for NATO enlargement beyond 2025 are constrained by three fundamental realities. Ukraine's accession is effectively frozen while active combat continues, despite growing interoperability and institutional integration. Georgia faces territorial disputes and political reversals that preclude membership in the medium term. Moldova's constitutional neutrality and Transnistria's frozen conflict create structural barriers to alliance membership. Meanwhile, existing members are prioritizing territorial defense over expansion, redirecting resources toward deterrence infrastructure along the alliance's current borders rather than extending security guarantees eastward.

This report provides a comprehensive analysis of these dynamics, examining the strategic calculations shaping NATO's future posture in Eastern Europe through 2035 and beyond.

Introduction

The question of NATO expansion in Eastern Europe has shifted from hypothetical strategic planning to immediate operational reality. Since Russia's full-scale invasion of Ukraine in February 2022, the security architecture of Eastern Europe has undergone its most dramatic transformation since the Cold War's conclusion. The alliance now confronts a fundamental strategic dilemma: should it extend membership to aspiring partners facing active Russian aggression, or consolidate its current frontiers through enhanced defense capabilities and deterrence infrastructure?

This question carries profound implications for European security. As of 2025, Bosnia and Herzegovina is the only country participating in a MAP, reflecting the narrowing pipeline of potential NATO members. Meanwhile, some intelligence agencies estimate that Russia could reconstitute its forces for a 'regional war' in the Baltic Sea area within two years of a potential ceasefire in Ukraine and for a 'local' one against a single neighbor within six months. This timeline compression creates acute pressure on alliance decision-making regarding future enlargement.

The strategic context differs fundamentally from previous enlargement rounds. During the 1990s and 2000s, NATO expansion occurred in a relatively permissive security environment characterized by Russian weakness and Western preponderance. Today, the alliance faces a revanchist Russia operating at wartime industrial capacity, uncertainty regarding American security commitments under shifting administrations, and internal divisions over burden-sharing and strategic priorities. President Trump urged NATO members to raise the Alliance's defense spending pledge from two percent to five percent of national GDP, with all except for Spain agreeing to spend 3.5 percent on regular defense and 1.5 percent on security-related measures by 2035.

This report examines the future of NATO expansion in Eastern Europe through multiple analytical lenses: the institutional pathways and obstacles facing current aspirants; the evolving threat environment and Russian military capabilities; the internal alliance dynamics affecting enlargement decisions; and the broader geopolitical context shaping strategic choices. The central question is not whether NATO should expand, but whether it can expand without compromising alliance cohesion, deterrence credibility, or the security of existing members.

Global and Regional Context

The broader European security environment has deteriorated markedly since 2022, fundamentally altering the context for NATO enlargement decisions. Russia's war against Ukraine represents the largest conventional military conflict in Europe since 1945, with profound implications for alliance strategy. Forty percent of Russia's 2025 federal budget, or almost eight percent of its GDP, was devoted to security and defense, sustaining the expansion of defense industrial production. This sustained mobilization indicates Moscow's long-term commitment to challenging Western security arrangements.

The geopolitical landscape surrounding potential NATO expansion has become increasingly complex. Russia has demonstrated willingness to use military force to prevent neighboring states from pursuing Western integration, having invaded Georgia in 2008, annexed Crimea in 2014, and launched full-scale war against Ukraine in 2022. The Russian Federation, led by its dictator, Vladimir Putin, is the single greatest threat to peace and democracy in Europe, having launched wars of conquest, invading his neighbors three times in the past 20 years. This pattern suggests Moscow views NATO enlargement as an existential threat justifying military intervention.

Meanwhile, the transatlantic relationship faces unprecedented strain. The Trump administration's approach to European security has introduced fundamental uncertainty regarding American commitment to Article 5 guarantees. President Donald Trump has at times signaled a positive view of Russian President Vladimir Putin's leadership and has repeatedly questioned the value of defending Europe, at one point telling reporters that he would 'encourage them [Russia] to do whatever the hell they want' to NATO allies that fail to meet defense spending targets. This rhetoric undermines the credibility of extended deterrence that has underpinned European security since 1949.

The regional security environment in Eastern Europe has become increasingly militarized. NATO's Exercise Dacian Fall 2025 engaged more than 5,000 troops and 1,200 units of equipment from ten Allied nations, demonstrating the alliance's enhanced forward presence. Concurrently, NATO launched Eastern Sentry to bolster its posture even further along its eastern flank in response to Russian drone incursions into Polish airspace. These deployments reflect a shift from crisis management to territorial defense as NATO's primary mission.

Economic factors also shape the enlargement context. European defense spending has increased substantially, with defence spending among EU countries reaching a new record of €343 billion, with member states increasing their investments by 19 percent between 2023 and 2024. However, this increase must be sustained over decades to meaningfully enhance capabilities. The fiscal burden of defense modernization competes with other priorities, particularly as European economies face structural challenges including aging populations, energy transition costs, and post-pandemic debt burdens.

The geopolitical competition extends beyond bilateral NATO-Russia dynamics. China's growing alignment with Russia, including provision of dual-use technologies and diplomatic support, creates a more complex strategic environment. Iran and North Korea provide direct military assistance to Russian forces in Ukraine, demonstrating the emergence of an anti-Western coalition spanning multiple regions. This broader confrontation between democratic and autocratic governance models affects calculations regarding NATO expansion, as enlargement becomes entangled in global power competition.

Furthermore, hybrid threats have proliferated across Eastern Europe. Russian intelligence services conduct sabotage operations, disinformation campaigns, cyber attacks, and political interference in both NATO members and aspiring partners. According to Elena Marzac, executive manager of the Information and Documentation Centre on NATO in Chisinau, 'it is too early to talk about the existence in Moldova of an integrated and effective national mechanism for preventing and combating cybersecurity incidents and cybercrime'. This vulnerability complicates enlargement by raising questions about whether aspirants possess adequate resilience to withstand Russian subversion.

Data and Evidence

The empirical foundation for assessing NATO expansion prospects rests on several key data points regarding military capabilities, defense spending, and institutional development. Defense expenditure trends provide the clearest indicator of both threat perception and enlargement feasibility. Poland stands out, with spending of $44.3 billion, reflecting its frontline position and heightened security concerns in Eastern Europe. This represents a defense burden exceeding 4 percent of GDP, more than double NATO's traditional 2 percent guideline.

The Baltic states demonstrate similar commitment levels. Poland has sharply increased its defence investment to nearly 3.8 percent of GDP, more than any other EU nation, with Estonia and Latvia following at 3.3 percent each, and Lithuania at 3.1 percent. These expenditure levels reflect existential threat perceptions among states neighboring Russia, contrasting sharply with Western European allies where defense spending increases remain more modest. The spending disparities suggest a fundamental divide within the alliance between frontline states prioritizing territorial defense and rear-area members viewing security more abstractly.

Russian military reconstitution provides critical context for enlargement timelines. Despite sustaining around 1.2 million battlefield casualties, Russia increased its army personnel by 234,000 in 2025, assembled a new army corps and motorised rifle division near Estonia in 2024, and formed 5 new divisions, 13 brigades, and 30 regiments in 2025. This force expansion indicates Moscow's determination to rebuild conventional capabilities even while sustaining combat operations in Ukraine. The scale and pace of Russian rearmament suggest that any post-Ukraine ceasefire would provide only a brief window before Moscow reconstitutes offensive capabilities threatening NATO's eastern flank.

Total NATO defense spending has reached unprecedented levels. Total military spending by NATO members amounted to $1,506 billion, or 55 percent of global military expenditure, with 18 of 32 NATO members spending at least 2.0 percent of GDP on their militaries in 2024. However, this aggregate figure masks significant variance. The United States accounts for 62 percent of NATO's total $1.59 trillion defense spending, underscoring persistent burden-sharing imbalances that fuel American skepticism regarding further security commitments in Europe.

Regarding specific aspirant countries, Ukraine has achieved substantial defense integration despite lacking formal membership. Ukraine became an Enhanced Opportunity Partner (EOP) in June 2020, a status offered to participants in NATO's Partnership Interoperability Initiative that have made particularly significant contributions to NATO operations, providing Ukraine preferential access to NATO's interoperability toolbox, including exercises, training, exchange of information and situational awareness. This deep cooperation demonstrates how NATO has developed mechanisms for security partnership short of formal membership guarantees.

Georgia's membership prospects face concrete obstacles. Georgia is not currently a member of NATO, but has been promised by NATO to be admitted in the future, yet Georgian president Salome Zourabichvili, who took office in 2018, has conceded that NATO membership might not be possible while Russia occupies Georgian territory, and has sought to focus on European Union membership, which Georgia submitted its application for in May 2022. This shift toward EU integration rather than NATO membership reflects pragmatic recognition of territorial integrity requirements for alliance accession.

Moldova presents a different profile. Moldova is a neutral country, with Article 11 of the Constitution stating: 'The Republic of Moldova proclaims its permanent neutrality. The Republic of Moldova does not allow the deployment of armed forces of other states on its territory'. However, Moldova has officially notified the secretariat of its withdrawal from the Commonwealth of Independent States and will stop participating in the organization in April 2027, becoming the third country to leave the CIS after Georgia and Ukraine. This suggests gradual Western reorientation despite constitutional constraints on NATO membership.

Public opinion data reveals ambivalence regarding NATO membership among aspirant populations. In February 2023, 24 percent of Moldovans would vote in favor of NATO membership while 62 percent would vote against, according to an IMAS poll. This domestic opposition creates political obstacles to membership even if NATO were willing to extend invitations. Similarly complex dynamics exist in Georgia, where Russian occupation of Abkhazia and South Ossetia undermines both territorial integrity requirements and public confidence in Western security guarantees.

Infrastructure development provides another metric for assessing enlargement readiness. The exercise marks a key milestone: the formal transition of NATO's battlegroups in Romania and Bulgaria to full brigade-level formations. This force posture enhancement indicates alliance focus on defending current members rather than extending security commitments to new territories. The substantial investment required for such infrastructure suggests opportunity costs associated with enlargement: resources devoted to integrating new members cannot simultaneously strengthen defenses along existing frontiers.

Core Analysis

The central analytical question regarding NATO expansion in Eastern Europe concerns the relationship between security provision and alliance sustainability. Extending membership to states facing active Russian military pressure creates immediate Article 5 obligations, potentially drawing NATO into direct conflict with a nuclear-armed adversary. Conversely, denying membership to partners under Russian threat undermines alliance credibility and potentially invites further aggression by signaling that Moscow can veto Western security architecture through military intimidation.

This dilemma manifests most acutely regarding Ukraine. While Ukraine could join NATO during the ongoing war with Russia, Ukraine joining the alliance during the invasion is extremely unlikely as NATO leadership worry Western troops could be drawn into a direct conflict with Russian forces, since Article 5 of the NATO treaty stipulates collective defense where an attack against one member is considered an attack against the entire block. This institutional logic creates a paradox: Ukraine needs NATO membership most urgently precisely when granting such membership carries maximum risk for existing allies.

NATO has attempted to resolve this paradox through graduated integration mechanisms. Members voted to simplify Ukraine's path to accession, removing the requirement for Kyiv to submit a 'Membership Action Plan', with one analyst noting that 'by removing that, essentially there is no other lock on Ukraine's membership to NATO but fundamentally a political decision by NATO leaders'. However, eliminating procedural barriers does not address the fundamental security dilemma. Political consensus among 32 member states remains elusive precisely because the stakes of Ukrainian membership are so high.

The underlying issue concerns extended deterrence credibility. NATO's security guarantee depends on the assumption that members will honor Article 5 commitments even at significant cost. However, Russia would likely unleash threats to use nuclear weapons to deter Western military assistance and undermine defender morale, with the objective being not territorial conquest but rather to force political concessions that undo the post-cold war security architecture in Eastern Europe, potentially presenting an ultimatum demanding removal of allied military presence and reimposition of military restrictions on NATO members that joined after 1997. This escalation dynamic raises profound questions about whether NATO members would risk nuclear confrontation to defend newly admitted allies facing Russian aggression.

American commitment uncertainty compounds these concerns. There are several pathways through which the United States may be unable or unwilling to intervene in Europe, including a large breakdown in transatlantic relations potentially driven by the Trump administration's approach to alliance politics, or a Russian limited incursion emerging as a war of opportunism if a large-scale interstate conflict in another part of the world were to curb Washington's capacity to project power in Europe. European allies lack autonomous capabilities to counter major Russian aggression without American participation, particularly regarding strategic enablers like intelligence, logistics, and nuclear deterrence.

The burden-sharing debate intersects directly with enlargement prospects. Existing members are struggling to meet enhanced defense spending targets, with core defense spending having doubled since 2019 and, under NATO's new 3.5 percent benchmark for 2035, potentially reaching about €800 billion by 2030, roughly 2.9 percent of GDP. Adding new members requiring substantial infrastructure investment and forward defense deployments would further strain already stretched defense budgets. The opportunity cost of enlargement becomes particularly acute when existing members require significant capability enhancements to deter Russian aggression against current NATO territory.

Territorial integrity requirements create another structural barrier. Following the 2014 annexation of Crimea by Russia, NATO officials warned that Russia might seek to annex Transnistria, a breakaway Moldovan region, with this separatist issue potentially precluding Moldova from joining NATO due to an unwillingness of alliance members to commit to defending a state which does not control its whole territory. This precedent extends to Ukraine's occupied territories and Georgia's Russian-controlled regions, creating a logical impossibility: these states need NATO membership because they face Russian aggression, yet Russian aggression makes them ineligible for membership.

The broader question concerns NATO's strategic orientation. The alliance faces a choice between horizontal expansion (adding new members) and vertical deepening (enhancing capabilities and readiness of existing members). Current evidence suggests prioritization of the latter. Phase one aligns with broader NATO efforts to reinforce its deterrence posture in Eastern Europe and enhance operational readiness amid evolving security dynamics. Substantial resources are being devoted to infrastructure, pre-positioned equipment, command and control systems, and force integration among current members rather than extending security guarantees eastward.

This strategic choice reflects threat assessment evolution. The alliance anticipates a conflict within the next decade, with the end of active combat in Ukraine potentially allowing Moscow to reposition significant military resources on its borders facing NATO's eastern flank. Under such threat conditions, alliance cohesion and defense effectiveness against current borders takes priority over territorial expansion that could overextend limited capabilities.

Future Scenarios

Scenario One: Frozen Enlargement and Fortress NATO (2026-2035)

In this baseline scenario, NATO effectively suspends further enlargement in Eastern Europe while dramatically enhancing territorial defense of existing members. Ukraine remains outside the alliance indefinitely despite continued security cooperation and military assistance. A negotiated settlement or frozen conflict emerges in Ukraine by 2027, with Russia retaining control over occupied territories. NATO responds by massively fortifying the eastern flank, with Germany stationing a full armored brigade permanently in Lithuania in 2025, representing the first permanent deployment of German military forces on foreign soil in peacetime since World War II, a move unthinkable just three years earlier, signaling a German strategic culture transformed by the Ukraine war.

Defense spending across European NATO members reaches 3 percent of GDP by 2030, enabling procurement of advanced capabilities including integrated air and missile defense systems, substantial armor and artillery forces, and enhanced logistics infrastructure. The alliance develops layered defensive positions across Poland, Romania, and the Baltic states, creating military infrastructure capable of blunting Russian conventional offensives. However, Ukraine, Georgia, and Moldova remain outside NATO, creating a permanent buffer zone between the alliance and Russia. This arrangement provides temporary stability but leaves aspirant states vulnerable to Russian pressure and gradually erodes NATO's credibility regarding its open-door policy.

Scenario Two: Conditional Integration and Hybrid Security Architecture (2026-2035)

This scenario envisions NATO developing novel security arrangements short of full membership for Eastern European aspirants. Ukraine receives explicit security guarantees from major NATO powers through bilateral treaties rather than Article 5 coverage, similar to arrangements the United States maintains with Israel or Taiwan. These commitments include arms provisions, intelligence sharing, and pledges to respond to Russian aggression without triggering automatic collective defense obligations. Moldova and Georgia enter enhanced partnership programs providing substantial military assistance and political support while respecting constitutional neutrality or territorial integrity constraints.

Concurrently, the European Union accelerates defense integration independently of NATO, creating a European pillar within the transatlantic relationship. EU member states develop rapid reaction forces, joint procurement mechanisms, and defense industrial cooperation that provides security architecture partially overlapping with but distinct from NATO structures. Ukraine joins the EU by 2030, receiving substantial economic integration and security cooperation through European rather than Atlantic frameworks. This hybrid architecture addresses some security needs of Eastern European partners while avoiding the escalation risks associated with NATO membership, though it creates coordination challenges and ambiguity regarding security commitments.

Scenario Three: Accelerated Expansion and Great Power Confrontation (2027-2032)

In this high-risk scenario, a decisive Ukrainian military victory by 2027 or comprehensive Russian collapse creates conditions NATO leadership views as enabling expansion. The alliance extends membership invitations to Ukraine and potentially Georgia, calculating that Russian weakness makes accession less dangerous than in previous years. However, Moscow views NATO enlargement as an existential threat, responding with aggressive hybrid warfare, nuclear posturing, and limited military operations designed to fracture alliance cohesion without triggering full-scale war.

Russian forces conduct limited incursions into Baltic states or provocative actions in the Black Sea, testing NATO's Article 5 commitment and attempting to demonstrate that Western capitals are unwilling to risk nuclear escalation over small territorial disputes. The alliance faces acute crisis management challenges, with internal divisions between members advocating robust military responses and those seeking diplomatic de-escalation. American security guarantees come under severe strain as European capitals question Washington's willingness to risk New York for Tallinn. This scenario potentially leads to NATO's first major internal crisis since its founding, with the possibility of alliance fracture if members prove unable to forge consensus on responding to Russian provocations against newly admitted allies.

Policy Implications

The trajectories outlined above carry profound implications for governments across the Euro-Atlantic area. For Eastern European NATO members, particularly Poland and the Baltic states, the period 2026-2035 will require sustained defense investment at levels unprecedented in peacetime. These frontline states must develop autonomous defensive capabilities sufficient to deter Russian aggression even with reduced confidence in American security guarantees. This necessitates not only procurement of advanced weapons systems but also development of territorial defense doctrines, civil defense preparations, and societal resilience against hybrid threats.

For aspirant states, particularly Ukraine, the policy implications involve difficult choices between pursuing formal NATO membership despite its apparent unattainability and accepting alternative security arrangements that provide meaningful deterrence without alliance membership. Ukrainian leadership must balance the symbolic and legal importance of NATO accession against the practical security benefits of bilateral security partnerships, EU membership, and continued Western military assistance. The risk is that single-minded focus on NATO membership prevents acceptance of alternative arrangements that could provide substantial security improvements even without Article 5 guarantees.

For Western European NATO members, the core policy challenge involves reconciling enhanced defense spending with fiscal constraints and competing domestic priorities. Germany, France, and the United Kingdom must fundamentally restructure defense budgets and force postures to provide credible deterrence on the eastern flank while simultaneously maintaining expeditionary capabilities for crisis management in other regions. This requires difficult resource allocation decisions and potentially controversial domestic political debates about defense prioritization over social spending.

For the United States, policy implications center on defining the level and nature of security commitment to European allies amid competing strategic priorities. American administrations must determine whether European security remains a vital national interest justifying substantial military presence and potential combat involvement, or whether burden-sharing arrangements can transfer primary responsibility for territorial defense to European allies while maintaining American nuclear umbrella and enabling capabilities. This fundamental strategic choice will shape transatlantic relations for decades.

For Russia, NATO's enlargement trajectory creates incentives affecting Moscow's strategic calculations. If Russian leadership concludes that NATO expansion is inevitable regardless of Russian actions, incentives for restraint diminish. Conversely, if Moscow perceives that military pressure successfully prevents NATO enlargement, incentives for continued aggression increase. Western policymakers must carefully calibrate approaches to avoid inadvertently strengthening Russian incentives for military adventurism while maintaining alliance credibility regarding its open-door policy.

Recommendations

1. Develop Graduated Security Architecture: NATO should formalize multiple tiers of security partnership beyond the binary of membership or non-membership. Enhanced partnership programs could provide substantial military assistance, intelligence sharing, and political support to aspirant states without extending full Article 5 guarantees. This approach acknowledges security needs of Eastern European partners while managing escalation risks associated with formal enlargement during periods of acute Russian aggression.
2. Prioritize Defense Investment in Current Members: Alliance resources should focus primarily on enhancing territorial defense capabilities of existing eastern flank members rather than pursuing expansion. Spending growth remains uneven, with the Baltics, Germany, and the Nordics moving faster than much of Southern Europe, implying that capability gains will emerge at different speeds across the continent. Addressing these disparities and ensuring robust collective defense of current NATO territory must take precedence over enlargement initiatives.
3. Establish Clear Membership Criteria Including Post-Conflict Requirements: NATO should explicitly define the conditions under which countries with frozen conflicts or occupied territories could achieve membership. This could include requirements for resolution of territorial disputes, demonstrated control over claimed territory, or alternative frameworks addressing occupation scenarios. Clarity regarding membership pathways, even if demanding, would provide aspirants with transparent roadmaps while preventing false expectations.
4. Strengthen European Defense Autonomy: European NATO members should accelerate development of autonomous defense capabilities including command structures, logistics networks, and strategic enablers currently dependent on American assets. This reduces vulnerability to shifting American political commitment while enhancing overall alliance capabilities. EU defense initiatives should complement rather than compete with NATO structures, creating redundancy in security provision.
5. Maintain Military Assistance to Ukraine Regardless of Membership Timeline: NATO members should continue substantial military support for Ukraine's defense against Russian aggression independent of membership decisions. This assistance serves alliance interests by degrading Russian military capabilities, demonstrating Western resolve, and preventing Russian territorial gains that would worsen NATO's strategic position. Security cooperation should not be held hostage to membership debates.
6. Develop Communication Channels with Russia for Crisis Management: Despite fundamental disagreements regarding European security architecture, NATO should maintain channels for crisis communication and incident prevention with Russian counterparts. The absence of such mechanisms increases risks of inadvertent escalation during military incidents. Professional military-to-military contacts, even in adversarial contexts, reduce dangers of miscalculation.
7. Prepare Public Opinion in Member States for Extended Deterrence Commitments: Alliance governments must undertake serious efforts to build domestic political support for collective defense obligations, particularly regarding new members in exposed positions. Public understanding of Article 5 commitments and willingness to bear costs of alliance membership will prove crucial during crisis scenarios. This requires sustained political leadership and public education regarding alliance purposes.

Conclusion

The future of NATO expansion in Eastern Europe beyond 2025 will be defined less by institutional processes than by strategic fundamentals: the balance between security provision and alliance cohesion, the credibility of extended deterrence amid nuclear threats, and the capacity of democratic societies to sustain defense burdens adequate for territorial defense. The aspirations of Ukraine, Georgia, and Moldova for NATO membership confront the hard realities of Russian opposition, American ambivalence, and European resource constraints.

The alliance faces a decade of consolidation rather than expansion. Current members must enhance their own defense capabilities, develop deterrence infrastructure along existing borders, and prepare for potential confrontation with a Russia emerging from the Ukraine conflict determined to revise the post-Cold War security order. Aspirant states must accept that NATO membership may remain beyond reach for the foreseeable future, seeking security through alternative arrangements including bilateral partnerships, EU integration, and indigenous defense development.

The broader trajectory points toward a more fragmented European security architecture, with formal alliance membership for some states, enhanced partnerships for others, and neutral or contested status for still others. This reflects the sobering reality that the brief post-Cold War moment when NATO expansion appeared both feasible and stabilizing has definitively ended. The challenge now is constructing security arrangements that prevent war while acknowledging that comprehensive solutions integrating all of Eastern Europe into Western institutions remain elusive. Whether this imperfect architecture proves sufficient to maintain peace will become clear in the turbulent decade ahead.