Introduction

Amidst growing geopolitical urgency, the Western Balkans – a region historically and culturally intertwined with the European project – remain in a prolonged state of accession limbo. The European Union’s (EU) enlargement policy in the Western Balkans has entered a longlasting phase of stagnation that can no longer be recognized as a procedural delay or a temporary political impasse. Rather, it constitutes a structural security vulnerability. While enlargement has historically functioned as one the EU’s most effective foreign policy instrument, anchoring democratic reform and stabilising post-conflict regions, its current paralysis significantly undermines both regional stability and the Union’s strategic credibility.

In the aftermath of Russia’s invasion of Ukraine, European leaders have rhetorically reframed enlargement as a geopolitical imperative. At the same time, political rhetoric in Brussels  continues to endorse EU enlargement. Geopolitical urgency is repeatedly referenced, yet implementation lags remarkably in the Western Balkans. It can be argued that enlargement  has been used more as a geopolitical stabilisation tool rather than a path to guaranteed membership and thus, the rhetoric of strategic necessity has not been translated neither into binding timetables nor substantial institutional progress.

The institutional architecture of the Union remains fundamentally unfit to support meaningful expansion. The EU’s internal structures are often a core barrier to enlargement, not only in terms of procedural complexity which means systemic inefficiency, but also due to a severe democratic deficit and political fragmentation. The persistence of unanimity requirements, veto politics, and internal fragmentation has created a widening gap between geopolitical ambition and decision-making capacity. As a result, a strategic grey zone has been created in Southeast Europe, where instability lasts and external influence expands. This paper argues that enlargement must be reconceptualised not as a long-term normative project but as an immediate instrument of European security governance requiring both institutional recalibration and operational innovation through phased security integration.

This paper will employ as illustrative cases Serbia and Kosovo. Serbia represents a paradigmatic case of strategic hedging enabled by enlargement paralysis. Formally committed to EU accession, Belgrade has simultaneously deepened political, military, and energy ties with Russia and expanded economic cooperation with China. This dual-track foreign policy is not simply a reflection of domestic preference but is structurally facilitated by the absence of credible and time-bound accession incentives. Kosovo presents a distinct but equally revealing case, in which institutional fragmentation within the EU itself constitutes the primary constraint. The continued non-recognition of Kosovo by five EU member states creates a fundamental inconsistency in the Union’s external policy, undermining both enlargement coherence and broader security coordination. Unlike Serbia, Kosovo does not pursue a strategy of geopolitical balancing; rather, it is structurally excluded from full participation in international and European institutions due to its contested status.

Enlargement Stagnation as a Structural Security Vulnerability

The Western Balkans occupy a critical geostrategic position within Europe’s immediate neighbourhood. Despite formal accession pathways, progress has been uneven and frequently blocked. Since Croatia’s accession in 2013 enlargement momentum has slowed considerably, contributing to what has increasingly been characterised as a crisis of credibility in EU conditionality.

This stagnation produces a series of interconnected security risks. First, it weakens deterrence credibility by undermining the EU’s ability to anchor candidate states firmly within its normative and strategic orbit. When accession timelines remain uncertain and politically contingent, incentives for alignment diminish. Second, it fragments strategic coherence by leaving a region geographically surrounded by EU member states institutionally disconnected from its governance structures. Third, it creates governance vacuums that enable external penetration through economic leverage, political influence, and informational operations.

External actors such as Russia, China, and Turkey actively exploit these conditions through infrastructure investments, soft loans, media influence, and diplomatic outreach, especially in Serbia, Bosnia-Herzegovina, and Montenegro. Despite this strategic fragility, the Western Balkan countries continue to engage in institutional reforms, often at considerable domestic political cost. These efforts have not been met with consistent incentives or binding timelines from Brussels. The accession process remains vague, over-bureaucratised, and prone to politicisation, contributing to a frozen accession process. Nevertheless, it should be highlighted that the rival powers’ capitalization role should be understood as contextual instead of causal. The primary driver of vulnerability lies within the EU. The central issue is not the presence of external influence but the absence of effective European integration mechanisms. Enlargement, in its current form, functions as a declaratory security policy without operational substance.

The Institutional Constraint: Unanimity and Veto Politics

The core institutional constraint lies in the EU’s reliance on unanimity in enlargement decision-making. Article 49 of the Treaty on European Union (TEU) explicitly requires unanimity in the Council for the admission of new member states. In practice, unanimity has extended beyond the final accession decision to encompass intermediate stages of the accession process, including the opening and closing of negotiation clusters. This “informal unanimity” allows individual member states to instrumentalise enlargement for bilateral or domestic political purposes. Cases like Bulgaria’s and Greece’s vetoes over North Macedonia or repeated blockages in the Serbia-Kosovo dialogue illustrate how national interests can prevail over collective strategic considerations.

The result is a structural bottleneck in which even limited disagreements can halt the entire enlargement process. In a security environment characterised by urgency and geopolitical competition, such institutional rigidity substantially constrains the EU’s capacity to act as a coherent strategic actor.

Recalibrating Decision-Making: Targeted Extension of Qualified Majority Voting

Addressing this constraint requires a recalibration of decision-making procedures. The targeted extension of Qualified Majority Voting (QMV) to specific enlargement-related decisions offers a pragmatic pathway that balances efficiency with political feasibility. Rather than challenging unanimity for final accession, reform should focus on intermediate procedural stages, where the costs of obstruction are highest relative to their political sensitivity. In legal terms, such a shift can be grounded in Article 48(7) TEU, the passerelle clause, which allows the European Council to authorise a transition from unanimity to QMV in defined policy areas without formal Treaty revision. While enlargement as a whole remains governed by Article 49 TEU, not all intermediate steps are explicitly bound by unanimity in primary law, creating scope for institutional differentiation between final accession decisions and preparatory or procedural measures.

QMV could be introduced for the opening and closing of negotiation clusters, progress assessments and benchmarking, as well as participation in EU programmes and security frameworks. This would reduce the capacity of individual member states to obstruct progress at early and intermediate stages without altering the legal requirement of unanimity for accession itself. Indeed, while unanimity may remain appropriate for sovereignty-sensitive decisions at the beginning and end of the accession process, applying QMV to intermediate stages would limit the abuse of veto power for domestic or bilateral purposes. Nevertheless, such reforms face significant political resistance from member states concerned with preserving national influence or leveraging bilateral disputes. Consequently, a realistic reform pathway requires adopting a hybrid approach, maintaining unanimity for final accession while introducing QMV in technical and procedural domains.

Phased Security Integration as Operational Strategy

Institutional reform alone is insufficient without a parallel transformation in how enlargement is conceptualised and implemented. The traditional accession model remains largely linear and binary, whereby states either achieve full membership or remain outside the Union. Instead, enlargement should be reconceptualised as a process of phased or gradual integration, allowing candidate states to be embedded progressively within the EU’s security and governance structures prior to full accession. Maintaining the traditional approach is increasingly unfit taking into account evolving geopolitical and security realities. Associate participation provides the conceptual foundation for this approach. It entails conditional and reversible inclusion of third states in EU policy frameworks without granting decision-making rights, thereby preserving both flexibility and conditionality.

The first phase of integration should focus on energy and cybersecurity. The Energy Community provides a legally binding framework for integrating Western Balkan energy systems into the EU internal market, including electricity market coupling, coordinated security-of-supply mechanisms, and participation in joint procurement initiatives, thereby reducing structural dependencies and enhancing resilience. In the case of Serbia for example, such integration would directly constrain reliance on Russian energy, thereby limiting its capacity to maintain a dual-track foreign policy. For Kosovo, enhanced integration would mitigate structural vulnerabilities associated with limited infrastructure and partial international recognition, strengthening both resilience and regional connectivity.

Cybersecurity integration would involve participation in EU-level coordination mechanisms, including those associated with the Cyber Diplomacy Toolbox and the European External Action Service. This would enable information sharing, joint response coordination, and participation in exercises, thereby strengthening resilience against hybrid threats. For Serbia, such integration would increase the political costs of strategic ambiguity by aligning it more closely with EU positions. For Kosovo, it would strengthen institutional resilience and enhance its capacity to counter hybrid threats, particularly given the region’s documented vulnerability to cyber and informational interference.

The second phase would extend integration into crisis management under the CSDP. Framework Participation Agreements provide an established legal basis for third-country involvement in EU missions, regulating participation through structured arrangements concluded under Articles 37 TEU and 218 TFEU. Expanding and institutionalising such participation would enhance interoperability and embed Western Balkan states within EU operational structures, particularly given the CSDP’s integrated civilian-military command system and its increasing openness to partner contributions. For Serbia, this would increase exposure to EU security norms and reduce strategic ambiguity. In the case of Kosovo, participation in CSDP frameworks building on existing missions such as EULEX would strengthen international legitimacy and facilitate coordination with both EU and NATO actors.

The final phase involves participation in PESCO projects. Council Decision (CFSP) 2017/2315 establishing PESCO, and subsequent Decision (CFSP) 2020/1639 on third-state participation, provide a legal framework for such involvement. Participation should initially focus on technical projects, such as military mobility and cyber capabilities, to minimise political resistance, as PESCO projects are primarily designed to deliver concrete military capabilities and enhance operational cooperation and interoperability rather than address sovereignty-sensitive political questions. Third-state participation is conditional upon alignment with EU values and security interests, as well as the ability to contribute substantively to specific projects, thereby embedding participants within EU defence structures without granting decision-making authority.

For Serbia, this participation is not merely hypothetical but institutionally plausible, as it already maintains an Administrative Arrangement with the European Defence Agency; a key legal prerequisite for third-state involvement in PESCO frameworks. Serbia is structurally positioned for such integration. Participation would therefore create concrete incentives for alignment and gradually constrain its capacity for strategic hedging. For Kosovo, due to the fact that participation requires formalised security agreements and political consensus among member states, even limited involvement would mark a significant step toward integration into European defence structures, partially offsetting the constraints imposed by its contested status.

Conclusion

The stagnation of EU enlargement in the Western Balkans represents a structural vulnerability within the European security architecture. The persistence of unanimity-based decision-making and the absence of intermediate integration mechanisms have created a strategic vacuum in Southeast Europe. A recalibrated approach, combining targeted extension of QMV with phased security integration, offers a legally grounded and politically realistic pathway forward. The cases of Serbia and Kosovo illustrate the potential benefits of a phased approach. By embedding candidate states within the EU’s security architecture prior to full membership, the Union can mitigate geopolitical risks while restoring credibility to its enlargement policy. These two dimensions are mutually reinforcing. Together, they provide a coherent framework for making enlargement an effective instrument of European security governance. Without institutional recalibration, enlargement will most likely remain a declaratory policy, undermining the EU’s strategic position. With the appropriate reforms, enlargement can once again serve as a central pillar of European security governance.