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Why Credible EU Membership Matters: How to Sequence Integration and Accession in Ukraine and the Western Balkans

At the 2026 Munich Security Conference, Ukrainian President Volodymyr Zelensky stated that Ukraine “needs a date” for EU accession. He warned that without a credible membership perspective, Russia would seek to obstruct Ukraine’s European future and stressed Kyiv’s objective of being ready to join by 2027.[1]

Zelensky’s appeal reflected a broader transformation in the role of enlargement. Following Russia’s full-scale invasion in 2022, EU enlargement rapidly shifted from a stalled and politically contested process to a central instrument of European security. Ukraine and Moldova were granted candidate status, Georgia received a European perspective and later candidate status. Meanwhile, accession negotiations with Western Balkan countries regained momentum. Ever since, enlargement has been increasingly used not only to prepare countries for membership, but also to strengthen resilience and anchor political alignment in a geopolitical environment shaped by war and strategic uncertainty.

Such a renewed strategic role of enlargement has exposed growing tensions within this policy itself. Granted, accession remains formally the central objective. Still, over recent years, the Union has increasingly relied on flexible forms of gradual integration to provide financial support, institutional access, political anchoring, and even foreign policy and defence cooperation well before membership. With formal accession remaining politically uncertain, uneven and subject to member state discretion, instruments such as the European Peace Facility, the Ukraine Facility and the Reform and Growth Facility for the Western Balkans have significantly expanded integration in practice.

Against this backdrop, renewed debate on whether enlargement requires new institutional models has sparked. Among others, proposals include staged accession,[2]Single Market integration as an intermediate status,[3] and more recently so-called reversed enlargement.[4] Such proposals seek to reconcile geopolitical urgency with the Union’s established accession framework. Russia’s war against Ukraine, growing geopolitical competition, and uncertainty surrounding the future of transatlantic security guarantees have increased the strategic importance of enlargement while also accelerating forms of integration that do not immediately lead to membership. Yet candidate countries have undertaken politically costly and socially disruptive reforms not simply because of the benefits of partial integration, but because such integration formed part of a credible and irreversible pathway to accession.

Under these conditions, the key question is not whether enlargement requires fundamentally new institutional models, but how to ensure that accelerated integration strengthens rather than replaces accession. This challenge takes different forms across regions. In Ukraine, gradual integration has become an essential instrument of state resilience under conditions of war.[5] In the Western Balkans, by contrast, the credibility of full membership remains indispensable to sustain political reform, particularly in areas such as the rule of law. Preserving credible accession while strategically sequencing gradual integration has therefore become central to enlargement’s effectiveness and to its role in strengthening European security.

The historical model of enlargement: Credible membership and gradual integration

EU enlargement has always been both geopolitical and merit-based. From its earliest rounds, accession served not only to integrate economies, but also to consolidate political alignment and stabilise Europe’s evolving security order. This was evident in the accession of the United Kingdom (1971), which took place in the context of the gradual dissolution of its empire and required significant economic adjustment and acceptance of the Community acquis, as well as in the enlargement to Greece (1981), Spain and Portugal (1986), which supported democratic consolidation and anchored these countries within the Western political and security order. Enlargement was thus never purely technocratic, but a political process structured through conditionality.

Over time, this political logic became institutionalised through a specific sequencing of gradual integration and credible membership. Accession was made conditional on the fulfilment of political, economic and legal criteria, while candidate countries were progressively integrated into parts of the Union’s regulatory framework. This allowed the EU to support domestic transformation while anchoring candidate countries functionally within its system even before accession.

This model became more formalised in the 1990s with the Copenhagen criteria and their operationalisation through structured accession instruments. The Europe Agreements granted Central and Eastern European countries progressive access to the EU’s market and policies in exchange for reforms, transforming gradual integration into a central instrument of enlargement. Crucially, these intermediate stages derived their effectiveness from being embedded within a credible pathway to full membership. Candidate countries implemented politically and economically costly reforms not simply to obtain partial integration benefits, but because these formed part of a broader and attainable accession trajectory.

This model was embedded within the broader Euro-Atlantic security architecture that emerged after the Cold War. NATO provided security guarantees, while EU enlargement anchored political and economic transformation. Together, they enabled the progressive integration of Central and Eastern European countries into the European and transatlantic order. In this context, gradual integration supported domestic reform and political alignment, while credible membership ensured that these efforts remained oriented toward full accession.

The effectiveness of enlargement therefore did not derive primarily from the design of intermediate integration stages, but from the credibility of membership itself. Gradual integration was effective because it was embedded within a political process whose endpoint remained clear and attainable. Enlargement succeeded not by substituting membership with partial integration, but by sequencing integration toward membership.

Structural transformations before 2022: Expanding integration, declining credibility

The post-2022 relaunch of enlargement built on structural transformations that had already reshaped the process well before Russia’s full-scale invasion of Ukraine. Over the previous two decades, enlargement progressively adapted to increasingly challenging candidate profiles, growing political contestation within the Union and a less permissive international environment. These shifts did not formally alter enlargement’s framework, but gradually weakened the alignment between gradual integration and credible membership that had underpinned its effectiveness.

First, the profile of candidate countries changed, and with it the function of enlargement. From the early 2000s onwards, enlargement increasingly involved post-conflict and structurally fragile states where stabilisation and reconstruction became immediate priorities alongside accession. In the Western Balkans, the EU used enlargement as part of a broader post-war strategy, providing financial assistance, market access and regulatory integration through the Stabilisation and Association Process well before membership became politically realistic. This approach was reinforced by regional and sectoral integration frameworks such as the Regional Economic Area and the Energy Community, which progressively extended EU rules and policies into the region. As a result, enlargement increasingly functioned as an instrument for stabilisation, governance and political anchoring even in the absence of a defined accession timeline.[6]

Second, enlargement became progressively more politicised and subject to tighter political control by member states. While accession had always required unanimity, from the mid-2000s onwards a succession of internal EU crises – including the constitutional crisis, the eurozone crisis, migration pressures and rule-of-law disputes – contributed to growing enlargement fatigue and greater political caution.[7] Governments exercised more direct control over negotiations, both through procedural reforms and through the increasing use of veto powers to pursue bilateral or political concerns, as illustrated by stalemates caused by Slovenia, Greece, France and Bulgaria. The introduction of the “fundamentals first” approach in the early 2010s and its consolidation in the revised enlargement methodology adopted in 2020 further reinforced the central role of political judgement of the EU member states.[8] As a result, while gradual integration continued to expand, accession became more politically contingent, less predictable and less credible as an attainable endpoint.

Third, enlargement operated within an international security environment that was initially permissive but became progressively more constrained and contested. In the Western Balkans, United States and NATO’s military presence ensured post-conflict stability, reducing the urgency of resolving open political and security issues through accession and allowing enlargement to function primarily as a tool of political and economic transformation while effectively relying on external security guarantees. Unlike in Central and Eastern Europe, where EU and NATO enlargement progressed in parallel, gradual integration in the Western Balkans could advance even as membership remained politically distant. Over time, however, this environment became less stable. Russia’s growing assertiveness after 2008 and increasing uncertainty surrounding US engagement exposed the limits of a model in which enlargement depended on external security guarantees. Episodes of transatlantic divergence – particularly during the Trump administrations – further highlighted the fragility of this framework and the risks associated with unresolved regional disputes, including Serbia–Kosovo relations and the structural fragilities of Bosnia and Herzegovina’s Dayton constitutional order. Enlargement increasingly operated in a contested geopolitical environment in which its stabilising function could no longer be separated from broader questions of European security.[9]

Taken together, these transformations progressively altered the internal balance of enlargement. Gradual integration expanded in scope and function, supporting stabilisation, governance and political alignment across multiple policy domains. At the same time, the credibility of membership declined as accession became slower, more contested and more politically uncertain. Enlargement increasingly operated as a framework for integration without accession, rather than as a structured political process in which integration and membership advanced together.

By the eve of Russia’s full-scale invasion of Ukraine, the formal framework of enlargement remained intact, but its political logic had begun to erode. Gradual integration continued to expand, while credible membership – the element that had historically given enlargement its transformative power – had become more uncertain. It was this growing imbalance, rather than the invention of new institutional models, that would shape the Union’s enlargement response after 2022.

Enlargement in a deteriorating security environment

Russia’s full-scale invasion of Ukraine in 2022 simultaneously relaunched enlargement as a formal accession policy and accelerated its evolution as a framework for integration short of membership. This dual acceleration exposed a structural tension that had been building for over two decades: while accession regained strategic urgency, integration increasingly developed with a degree of autonomy from formal membership.

A process whose credibility had progressively weakened over the previous decade was rapidly reactivated as part of the Union’s response to war and geopolitical confrontation. In a series of decisions unprecedented in recent years, the European Council granted candidate status to Ukraine and Moldova, recognised Georgia’s European perspective and subsequently granted it candidate status, and revived accession negotiations with Western Balkan countries. Unlike in the previous decade, when even indicative accession timelines were politically dismissed,[10] EU leaders once again began framing enlargement as a concrete political objective. Despite continued blockages, including repeated Hungarian vetoes, member states and EU institutions demonstrated greater willingness to actively overcome obstacles than in the past, signalling renewed political commitment to enlargement.[11]

At the same time, enlargement further expanded its role as a framework for advancing substantial integration short of membership. Ukraine represents the most advanced expression of a dynamic already visible in the Western Balkans, but under far more demanding conditions. Faced with ongoing war, gradual integration became directly linked to the Ukrainian state’s economic stability, institutional continuity and defence capacity. The EU opened its budget to a candidate country on an unprecedented scale, providing sustained macro-financial assistance, expanding access to EU programmes and establishing dense political coordination through instruments such as the Ukraine Facility. In parallel, NATO and bilateral commitments remained central to Ukraine’s defence, while EU instruments such as the European Peace Facility supported its military capabilities and defence industrial integration. Enlargement thus operated alongside NATO as part of a broader framework of strategic anchoring, combining accelerated integration with external security cooperation provided primarily through NATO and bilateral arrangements.

These dynamics were equally visible in the Western Balkans, where both accession and material integration regained momentum. The restoration of enlargement’s political credibility translated into tangible progress where domestic conditions allowed. Montenegro overcame a prolonged stalemate after receiving a positive Interim Benchmark Assessment Report (IBAR) on rule of law reforms in June 2024, enabling negotiations to resume after years of paralysis. It has now opened all negotiating chapters and provisionally closed 13 of 33, marking the most significant progress in over a decade.[12]Albania also advanced rapidly following the opening of accession negotiations in 2022. After years of political blockage unrelated to its reform performance, it began opening negotiating clusters in 2024 and is now negotiating across all clusters of the EU acquis.[13] These developments demonstrated that enlargement retains its transformative capacity when supported by credible accession prospects.

Material integration also deepened across the region. Instruments such as the Reform and Growth Facility expanded financial support, economic integration and policy coordination, strengthening institutional resilience while accelerating functional incorporation into key EU frameworks prior to membership.[14]

At the same time, enlargement continued to shape geopolitical alignment. Albania, Montenegro, North Macedonia and Kosovo aligned closely with EU foreign policy positions, including sanctions against Russia, reflecting their clear strategic orientation toward accession. Even where alignment remained incomplete, accession dynamics exerted structural influence. Serbia, for example, did not formally align with EU sanctions but supported Ukraine’s territorial integrity, allowed Serbian-produced ammunition to reach Ukraine indirectly, and gradually reduced aspects of its defence cooperation and energy dependence on Russia.[15]

Taken together, these developments illustrate both the renewed strategic centrality of enlargement and the internal tension generated by its accelerated use under conditions of war. Russia’s invasion has not only revitalised accession as a political objective, but also expanded gradual integration as an immediate instrument of stabilisation, resilience and geopolitical alignment. Without clearer political sequencing between integration and accession, though, enlargement risks evolving into a framework primarily suited to crisis management and short-term stabilisation, but insufficient to generate the durable political and structural transformation necessary to underpin European security. Preserving enlargement’s effectiveness will therefore depend not simply on expanding integration, but on ensuring that such integration remains credibly oriented toward full membership, which continues to sustain reform, enable lasting transformation and anchor long-term security.

Recalibrating enlargement: Bridging formal accession and material integration

Russia’s invasion of Ukraine and the parallel acceleration of the accession process and gradual integration have intensified a structural tension between the formal and material dimensions of enlargement. While accession has regained political visibility and momentum, gradual integration has expanded more rapidly, assuming immediate geopolitical, economic and security functions. Enlargement has thus increasingly operated as a framework for resilience and political anchoring even where membership remains uncertain. This has revived debates on whether fundamentally new institutional models are needed to reconcile accelerated integration with a slower and more politically contingent accession process.

Several proposals have emerged in response. Some advocate granting selected candidate countries full participation in the Single Market as an intermediate status, allowing integration to advance independently of accession timing.[16] This approach has recently gained political support from some candidate countries themselves. In February 2026, Albanian Prime Minister Edi Rama and Serbian President Aleksandar Vučić jointly called for granting Western Balkan countries access to the EU Single Market and key policies prior to full membership.[17]

Others propose more structured forms of staged accession.[18] This model seeks to formalise gradual integration by dividing the accession process into clearly defined intermediate stages, each associated with specific rights, obligations and benefits. Progression between stages would be more directly linked to reform performance, strengthening the credibility of conditionality and providing more continuous incentives for reform. Crucially, staged accession also blurs the institutional boundary between membership and non-membership by allowing candidate countries to progressively acquire selected rights and participate in EU institutions before formal accession, while withholding full voting rights until the final stage.

More recently, proposals for so-called reversed enlargement have suggested that formal membership itself could precede full integration, particularly in the context of ongoing peace negotiations and discussions over Ukraine’s future security guarantees. Ukrainian and European leaders have explored how EU membership could contribute to Ukraine’s long-term political anchoring and post-war security architecture, including in discussions with transatlantic partners. In this model, accession would occur earlier, while extensive transitional arrangements, opt-outs and conditional access to specific EU policies would allow integration to continue after membership. This approach has begun to inform internal discussions within EU institutions, including the European Commission, as part of broader efforts to reconcile enlargement with a more unstable European security environment.[19]

These models respond to distinct but interrelated structural challenges. Single Market integration primarily seeks to mitigate the declining credibility of accession caused by internal political volatility within the Union, by providing candidate countries with a concrete and less politically contingent integration objective. Staged accession aims to address the growing complexity and fragility of candidate countries by strengthening the link between reform performance and institutional rewards while progressively bridging the gap between membership and non-membership. Reversed enlargement responds instead to acute geopolitical pressures, particularly in Ukraine, by treating membership itself as a strategic anchoring instrument under conditions of heightened security uncertainty.

Yet the central challenge facing enlargement today is not primarily institutional, but political: restoring coherence between its material integration and its membership promise. The Union already possesses the instruments needed to advance gradual integration, support resilience and manage differentiated trajectories. Ukraine illustrates how substantial integration can proceed rapidly even in the absence of membership, contributing directly to economic stability, institutional continuity and geopolitical anchoring. Ukraine’s long-term security will depend less on formal EU membership clauses than on sustained military support, defence capabilities and credible security guarantees, which remain primarily anchored in NATO and bilateral commitments. Advancing Ukraine’s integration into the Single Market therefore represents a functionally coherent pathway for sustaining convergence while broader security conditions remain uncertain, without requiring politically premature decisions on full membership.

By contrast, preserving the credibility of accession is most urgent in the Western Balkans. There, membership continues to function as the primary driver of political reform, particularly in core areas such as the rule of law. Recent progress in Montenegro, following a positive Interim Benchmark Assessment Report, and Albania’s rapid opening of negotiating clusters demonstrate how credible accession prospects can restore reform momentum after prolonged stagnation. The prospect of membership strengthens reform-oriented political coalitions and reinforces the EU’s leverage in supporting structural transformation. This political dynamic cannot be replicated through technical integration alone.

At the same time, gradual integration remains essential in the Western Balkans to manage the long post-accession adjustment period and prevent the emergence of new divisions within the region. Full alignment with the acquis in areas such as energy, environment and agriculture will require massive investments and extended transitional arrangements well beyond formal membership. As frontrunners such as Montenegro and Albania move closer to accession, strengthening regional integration and expanding progressive access to the Single Market will be critical to ensure that differentiated accession reinforces convergence rather than creating new internal borders. Instruments such as the Growth Plan will be critical to ensure that differentiated accession reinforces convergence rather than institutionalising fragmentation.

The central issue facing enlargement today is therefore not the need to reinvent its institutional framework, but to strategically recalibrate the relationship between integration and accession. Enlargement has always relied on the interaction between gradual integration and credible membership to reconcile its geopolitical function with its merit-based logic. Its effectiveness now depends on sequencing these instruments appropriately: using accelerated integration to strengthen resilience where necessary, particularly in Ukraine, while preserving credible and achievable accession pathways where membership remains the primary driver of transformation, particularly in the Western Balkans.[20] Without such political sequencing, enlargement risks evolving into an open-ended framework for integration without accession, weakening both its transformative power and its strategic role in European security.


Matteo Bonomi is Senior Fellow in the “EU, politics and institutions” programme at the Istituto Affari Internazionali (IAI).
This brief was produced by the Istituto Affari Internazionali as part of the InCLUDE project, supported by Open Society Foundations Western Balkans. Its contents are the sole responsibility of the author and do not necessarily reflect the views of Open Society Foundations Western Balkans.

[1] Paternoster, Tamsin et al., “Munich Security Conference: Zelenskyy Says Ukraine ‘Needs Date’ for EU Accession, Aims for 2027”, in Euronews, 14 February 2026, https://www.euronews.com/my-europe/2026/02/14/munich-security-conference-rubio-to-give-speech-as-leaders-gather.

[2] Mihajlović, Milena et al., Template 2.0 for Staged Accession to the EU, Belgrade/Brussels, European Policy Centre/Centre for European Policy Studies, August 2023, https://www.ceps.eu/?p=40577.

[3] European Stability Initiative website: Offer the Four Freedoms to Ukraine, Moldova and the Balkans. For a Merit-based EU Accession Process with a Credible Goal, https://www.esiweb.org/taxonomy/term/2377; and recent op-ed by Albanian Prime Minister Edi Rama and Serbian President Aleksandar Vučić, “Das wäre ein realistischer Weg in die EU”, in Frankfurter Allgemeine Zeitung, 28 February 2026, https://www.faz.net/aktuell/politik/ausland/serbien-und-albanien-ein-realistischer-weg-in-die-eu-accg-110845507.html.

[4] Sheftalovich, Zoya, “5 Steps to Get Ukraine into the EU by 2027”, in Politico EU, 10 February 2026, https://www.politico.eu/?p=7910388.

[5] This brief focuses on Ukraine and the Western Balkans. Georgia’s accession process is currently stalled amid political tensions with the EU and concerns over democratic backsliding. Moldova, while highly relevant, follows a distinct trajectory and is not examined here.

[6] Bonomi, Matteo, “Enlargement as Milieu Governance in the Western Balkans”, in Sonia Lucarelli and James Sperling (eds), Handbook of European Union Governance, Cheltenham/Northampton, Edward Elgar, 2025, p. 445-458, DOI 10.4337/9781803925189.00045.

[7] Hillion, Christophe, “The Creeping Nationalisation of the EU Enlargement Policy”, in SIEPS Reports, No. 2010:6 (November 2010), https://sieps.se/en/publications/2010/the-creeping-nationalisation-of-the-eu-enlargement-policy-20106.

[8] Tilev, Dragan, The New EU Enlargement Methodology: Enhancing the Accession Process, IDSCS, March 2020, https://idscs.org.mk/en/?p=18722.

[9] Amadio Viceré, Maria Giulia and Matteo Bonomi, “External Differentiation as a Strategy of System Maintenance: EU Enlargement towards the Western Balkans”, in West European Politics, Vol. 48, No. 5 (2025), p. 1159-1185, https://doi.org/10.1080/01402382.2024.2401298.

[10] Gray, Andrew, “Macron Pours Cold Water on Balkan EU Membership Hopes”, in Politico EU, 17 May 2018, https://www.politico.eu/?p=890316.

[11] “EU Summit: Germany’s Scholz Gets Orbán to Leave Room for Decision on Ukraine Accession”, in Euronews, 16 December 2023, https://www.euronews.com/2023/12/16/eu-summit-germanys-scholz-gets-orban-to-leave-room-for-decision-on-ukraine-accession.

[12] European Commission DG for Enlargement, EU and Montenegro Provisionally Close Another Chapter in Accession Negotiations, 26 January 2026, https://enlargement.ec.europa.eu/node/5597_en.

[13] European Western Balkans, Albania Opened the Last Remaining Cluster with the EU, 17 November 2025, https://europeanwesternbalkans.com/?p=55526.

[14] Bonomi, Matteo, “Integrating the Western Balkans with the EU Economy: New Plan, Old Problems”, in Stormy-Annika Mildner et al. (eds), Structural Change in the Western Balkans, Berlin, Aspen Institute Germany, December 2025, p. 13-22, https://www.aspeninstitute.de/wp-content/uploads/Structural-Change-in-the-Western-Balkans.pdf.

[15] Todorović, Marko, “Long Policy Report on Russia’s Ambitions and Leverage”, in InvigoratEU Deliverables, No. 6.1 (May 2025), https://zenodo.org/records/17338235.

[16] European Stability Initiative website: Offer the Four Freedoms to Ukraine, Moldova and the Balkans. For a Merit-based EU Accession Process with a Credible Goal, https://www.esiweb.org/taxonomy/term/2377.

[17] Rama, Edi and Aleksandar Vučić, “Das wäre ein realistischer Weg in die EU”, cit.

[18] Mihajlović, Milena et al., Template 2.0 for Staged Accession to the EU, cit.

[19] Sheftalovich, Zoya, “5 Steps to Get Ukraine into the EU by 2027”, cit.

[20] Similar considerations may also apply, in part, to Moldova, whose accession trajectory shares several structural features with the Western Balkans, even though it presents distinct political and security dynamics beyond the scope of this brief.