The Risks of a Reinvigorated EU-Western Balkans Defence Cooperation

This CIDOB Briefing examines the European Union (EU)’s evolving approach to enlargement in the Western Balkans. It identifies three key risks that have surfaced as enlargement has been linked with defence agendas to meet geopolitical priorities: the erosion of the EU’s normative power, regional fragmentation and potential conflict escalation. The Briefing concludes with targeted policy recommendations to address these challenges and strengthen a cohesive, regionally integrated strategy.

Introduction

The Western Balkans, previously sidelined by a stalled enlargement agenda, have returned to the centre of European Union (EU) attention. Geopolitical pressures push the Union to integrate security and defence into its relations with the region. Driven by the urgency and threats posed to the EU’s borders by Russia’s war against Ukraine, shifting United States foreign policy priorities and increased foreign interference, such as by China or Russia, enlargement has become a key geopolitical tool, now explicitly tied to broader agendas of security and defence. 

This geopolitical reframing has energised the EU’s activity in the region and is reflected in the proliferation of institutional and civil society events – from the EU Enlargement Forum to various EU-Western Balkans Summits and next year’s Enlargement Conference. This political momentum is also translated into policy, as illustrated by the 2025 Enlargement Package, which evaluates the yearly progress of (potential) candidate countries towards EU integration. Among the ten country reports, six concern the Western Balkans, underscoring the region’s strategic relevance and noting continued (and uneven) progress in aligning their foreign policies with the EU’s Common Foreign and Security Policy. By linking EU membership prospects to these reforms, enlargement is being leveraged to strengthen defence cooperation, or even to advance ambitions of a future European defence union. 

Yet, the integration of the EU’s modernisation logic – centred on enlargement and support of liberal and democratic reforms - and new geostrategic logic – centred on military security and defence - is far from straightforward. While progress in defence cooperation with Western Balkan partners may boost their capacities to counter risks and threats on the Eastern border, this emerging defence-enlargement agenda does not automatically bring these countries closer to EU integration. 

This raises a critical question: what risks emerge when moving from an ‘ever closer Union’ to an ‘(ever) larger Union’ under shifting security imperatives? This CIDOB Briefing outlines the EU’s new enlargement approach in the Western Balkans in which defence and enlargement agendas are increasingly intertwined, discusses three main risks – the erosion of the EU’s normative power, regional fragmentation and conflict escalation – and offers policy recommendations for developing a more coherent, regional lens for a joint enlargement and defence strategy. 

A new approach to the Western Balkans

Enlargement is one of the EU’s longest standing and most successful policies for providing stability, democracy, peace and security across the continent. It paved the way for the creation of the EU27 as we know it today: successfully consolidating liberal democracy in countries with authoritarian and socialist pasts, and in those divided by disputed borders or armed conflict. After Croatia’s accession in 2013, however, the momentum behind enlargement stalled. The Western Balkans, once promised unequivocal support for their European perspective at the 2003 Thessaloniki Summit, found themselves in a prolonged waiting room, with little progress and growing frustration. This stagnation has led to what has been described as a “credibility dilemma”: Member States grew wary of the risks associated with further enlargement, whereas candidate countries doubted the EU’s political commitment. With an increasingly technical and fraught process, public support in the Western Balkans waned, as citizens became disillusioned with the promise of entering the Union. 

As the EU sought to reactivate the enlargement process under the first Von der Leyen Commission – through initiatives such as the Economic and Investment Plan, and diplomatic commitments in the region under then HR/VP Josep Borrell – Russia’s invasion of Ukraine in 2022 marked a watershed moment for the EU. Within weeks, Ukraine, Moldova, and Georgia applied for EU membership, and by the end of 2022, Ukraine, Moldova and Bosnia and Herzegovina were granted candidate status while accession negotiations opened for Albania and North Macedonia. In parallel, the New Growth Plan for the Western Balkans – worth €6 billion – was implemented to boost economic growth, and in 2023, a normalisation agreement was signed between Kosovo and Serbia.

The EU’s new impetus, however, is underscored by a geopolitical logic, superseding the previous vision of political enlargement: the Union is seeking to stabilise its borders and securitise against external threats. In view of the Russian challenge and the United States’ uncertain commitment to European security, defence alignments with the region have gained traction. Under the EU’s 2022 Strategic Compass and White Paper for European Defence – Readiness 2030, the Western Balkans are highlighted as a region of concern, vulnerable to potential Russian destabilisations and spillovers from the deterioration of European security. In this vein, the Western Balkans are increasingly seen as proactive contributors to European defence that can promote European security through their strategic location, as well as their existing industrial base, dual-use infrastructure, and expertise in producing military assets. 

Today, increased defence cooperation between the EU and the Western Balkans is viewed as a key opportunity to bring the region closer to the Union and thus, integrate the enlargement and defence agendas. Here, several flagship initiatives have been implemented. In 2024, the EU signed the Security and Defence Partnerships (SDP) with Albania and North Macedonia to enhance their participation in EU military and civilian missions and within the EU’s defence architecture – notably within the European Defence Agency and the Permanent Structured Cooperation (PESCO) projects. In parallel, the Security Action for Europe (SAFE) instrument within the Strategic Compass – though still pending formal enforcement – would allow candidate countries to participate in joint defence procurements with EU Member States and like-minded partners. In addition, the 2024 Critical Raw Materials Act – among other goals – is contributing to expanding the EU’s defence and military industries by reducing dependencies on Russia and China. Notably, the EU’s strategic partnership with Serbia – signed in June 2025 and identified by NATO as a critical defence project – grants access to key lithium and boron reserves. 

This renewed engagement extends beyond the EU level. Member States, while acting in coordination with EU defence objectives, have expanded their own arrangements with the Western Balkans. Indeed, most have technical-level agreements for capacity building initiatives and training, or directly supply military equipment to the region. For instance, the April 2025 Serbia-Hungary agreement for defence cooperation seeks to expand joint military exercises, arms procurement and training. Similarly, some Member States have renewed multilateral engagement to promote defence cooperation. A notable example is the Albania-Croatia-Kosovo joint Tirana Declaration of cooperation on defence, signed in Tirana in March 2025, whose aim is to jointly respond to hybrid threats. 

The EU’s narrative is unequivocal: increased defence investments in the Western Balkans will enhance their integration into the Union.  Defence cooperation has become means to progress the EU’s defence readiness as well as to overcome enlargement fatigue. In the current geopolitical landscape, defence collaboration is an additional rationale for accelerating accession, restoring credibility in the EU’s commitment to the Western Balkans, and promoting mutual trust – all the while countering Russian influence and a potential US disengagement.

Overshadowed Risks

Although enlargement and defence cooperation are often portrayed as mutually reinforcing – and defence has become a central concern amid geopolitical instability and war – three unanticipated risks arising from this strategy warrant attention: erosion of the EU’s normative power, regional fragmentation and conflict escalation.

The EU’s enhanced defence cooperation may erode the Union’s legitimacy and normative power in the Western Balkans. For decades, the EU’s external action in the region was grounded in a modernisation logic: promoting peace, democracy, human security, and economic development as the foundations for long-term stability and integration. The Stabilisation and Association Process (SAP), launched in 1999, exemplified this approach, aiming to reform governance and support European integration through the gradual adoption of EU norms and institutions to tackle the region’s challenges. In recent years, however, this agenda has been overshadowed towards a pragmatic one that focuses on countering external risks, prioritising strategic interests, and responding to a complex international environment – often at the expense of liberal norms. For instance, accession processes increasingly focus on stabilisation and countering external threats, effectively sidelining democratic transformation. Moreover, in prioritising strategic interests, the EU’s engagement in the Western Balkans is becoming transactional and sector-specific – as in the case of migration management and hybrid threats. Ultimately, the region is increasingly viewed as a geopolitical chessboard by external actors, and the EU competes for influence with other powers such as Russia, China, and Turkey.

The EU’s prioritisation of defence cooperation is further alienating the modernisation logic that once underscored its policies in the Western Balkans. For instance, the EU’s push to secure a critical raw materials project in Serbia while overlooking local concerns and illiberal practices, is contributing to the erosion of national public trust and reinforcing anti-EU sentiment – thus undermining its democratisation and Europeanisation prospects. Across the region, the EU’s credibility and commitment to the Western Balkans is weakening. There is growing public disillusionment that EU defence cooperation is short-term, insincere and creates unequal partnerships that prioritise the Union’s interests. Public trust is waning, as the perception of the Western Balkans as a permanent “buffer zone” rather than an integral part of Europe persists. Eventually, while citizens still aspire to a European future, it is less out of enthusiasm for the Union but more because they believe the alternatives are worse. 

European concerns about defence are still primarily driven by Member States' interests and by military needs, rather than embedded into broader security concerns related to peace, development and human security. Hence, it weakens the EU’s capacity to promote a modernisation agenda in the Western Balkans. While military cooperation is not necessarily at odds with peace and security, it contains certain risks that cannot be overlooked, particularly given the fragmented way in which it is currently taking place. 

A second risk is indeed the potential for heightened regional fragmentation. Traditionally, the EU contributed to sustaining regional integration by promoting interdependencies between the Western Balkans. For instance, forums like the 2014 Berlin Process sought to increase regional cooperation, while the Belgrade-Pristina dialogue strived to facilitate peace through the normalisation of relations between Serbia and Kosovo. Similarly, the EU-led connectivity projects in the Western Balkans aimed to reduce regional disparities and create cohesion – such as through the establishment of railway lines and roads. 

However, the ongoing developments in EU–Western Balkans defence cooperation lack a regional perspective that used to be the core makeup of EU policies. The current preference seems to be for tailored partnerships that adapt to the specific contexts and histories of the countries, even if they are addressing common and interconnected threats. For the EU, a one-size-fits-all solution is perceived as ineffective, as the Western Balkans countries have different interests with the EU, different political wills, different capabilities, and different ties with Russia. Yet, this approach is inadvertently contributing to regional fragmentation. For instance, Member States like Croatia and Hungary are forging their own partnerships with different groups of Western Balkan countries and competing for security investments and interests. Moreover, five Member States do not recognise Kosovo’s independence, hindering the EU-led Belgrade-Pristina dialogue. Similarly, the region remains divided between NATO members such as Albania, Montenegro and North Macedonia, and between EU Member States, candidates and potential candidates. An EU-tailored approach to the countries of the region, alongside bilateral or trilateral Member States initiatives, creates a complex constellation of policies within an even more complex architecture of allegiances. Despite the EU and Member States presenting these initiatives as mutually reinforcing, they risk duplicating efforts on the ground and creating a fragmented web of partnerships. And thus, create imbalances that drive different speeds of cooperation and generate tensions, thereby intensifying the anxieties of Western Balkan countries. 

This strategy is further exacerbated by the reactive nature of the EU’s defence cooperation with the region. The EU has prioritised salient or political expedient threats to enhance collaboration – such as migration, organised crime and terrorism – until new ones arise. This has limited policy continuity and the capacity to structurally tackle long-term security challenges, while focusing on EU security priorities as opposed to those of the Western Balkans. In a similar vein, zones of fragmentation are used by external actors to exert their influence at the same time as weakening EU-Western Balkan relations. For instance, Russia has long maintained a foothold in the region through its close ties with Serbia and endorsements of its strategic partnership and military cooperation. Similarly, China has economically invested in Serbian defence and military infrastructures, while Turkey is contributing to Kosovo’s militarisation. The complex and diverse geography of relations in defence with the Western Balkans is not only intensifying regional fragmentation, but may unwillingly feed narratives of conflict. 

A third risk therefore concerns the increased potential for conflict escalation in the Western Balkans, exacerbated by selective bilateral defence cooperation within the region. Initiatives to strengthen defence ties among only some partners – such as the Tirana Declaration signed by Albania, Croatia and Kosovo – have been perceived as exclusionary and provocative by excluded parties, in this case Serbia. The agreement, which aims to enhance defence capabilities among the signatories through, joint trainings and exercises, was denounced by Serbian president Aleksander Vučić as a violation of the 1996 Subregional Arms Control Agreement - i.e., a derivative of the Dayton Peace Agreement designed to regulate military activity and build confidence among Bosnia and Herzegovina, Croatia, Serbia and Montenegro. Historically, this accord has been key in ensuring transparency and trust; however, its recent politicisation and potential violation risks reviving old grievances and sparking a renewed arms competition. 

The Tirana Declaration also touches on another highly sensitive issue within the Western Balkans: the historical tensions between Serbia and Kosovo. While Kosovo presents the initiative as a transparent defence agreement, Serbian officials interpret it as a threat to sovereignty, invoking the need for defensive measures. Kosovo’s 2023 acquisition of Bayraktar drones from Turkey, along with potential domestic drone development, had already previously intensified Serbian fears of a militarized Kosovo. These developments risk further reactivating unresolved tensions which may undermine collective security objectives.

Although much of this contestation remains rhetorical, Serbia has responded by strengthening parallel defence cooperation with Hungary and Slovakia, including joint exercises, arms procurement and military education. While officials claim these initiatives are unrelated to the Tirana Declaration, their timing and scope suggest they are reactions to perceived encirclement. This suspicion is reciprocal: such alignments exacerbate the longstanding rivalry between Croatia and Serbia, which periodically fuels episodes of arms races and military competition. 

Selective defence cooperation can, rather than fostering cohesion, destabilise the already fragile regional security architecture within the Western Balkans. Politicising past grievances and agreements risks escalating conflict by feeding historical rivalries and renewed military competition. New alignments may create competing military blocs, exacerbate mutual distrust and undermine previous EU-led confidence-building measures. The EU maintains that integration and cooperation are inherently positive, as reflected in their Strategic Compass and NATO’s Strategic Concept, and views bilateral partnerships between member states and candidate countries as helpful for deeper alignment. However, uneven implementation and politicisation can turn well-intentioned initiatives into sources of instability. 

In sum, a defence and enlargement strategy that is incoherent, fragmented or selective, risks reproducing the same patterns of distrust, fragmentation and competition across the region. Addressing these risks requires a nuanced, regional approach that balances new geostrategic imperatives with human security, integration and confidence-building measures.

Policy Recommendations

To limit the risk of defence cooperation eroding the EU’s modernisation approach to the Western Balkans, the EU should prioritise its normative commitment towards development, peace, and human security. Practically, this could take the form of several initiatives that promote democratic support and economic interdependence, with the prospect of enlargement. For instance, emphasising policy formulas that have been successful in regional confidence building – such as the 1996 Subregional Arms Control Agreement – could prove pivotal in ensuring a balanced approach to defence cooperation. Similarly, embedding policy clauses for human security within a larger defence cooperation framework may create a form of “positive conditionality”. Whereby it ensures that increased defence investments do not come at the expense of peace and the full spectrum of security. Such approaches can not only foster a more mindful approach to defence collaboration, but can also help rebuild citizens’ trust on the Union, while meeting the Western Balkans’ demands for pragmatic policies that meet their socio-economic priorities.

To counter growing regional fragmentation, the EU must move beyond its reactive, crisis-driven approach and the assumption that tailored, country-specific policies automatically foster cohesion. Instead, it should adopt a cohesive regional framework for defence and enlargement cooperation. This framework could involve coordinating bilateral initiatives by member states and candidates by fostering joint planning, interoperable capabilities, and establishing shared priorities across the entire Western Balkans. By promoting long-term, region-wide collaboration rather than isolated partnerships, the EU can reduce duplication and fragmentation while creating more predictable and regionally beneficial security arrangements. Complementary measures, such as transparent reporting on defence initiatives and progress tracking, may further enhance accountability and consolidate regional coordination and agreed priorities.

Lastly, to mitigate the risk of reviving ethno-nationalist tensions and escalating conflict, the EU should promote a renewed spirit of cooperation and arms control within its regional framework. This requires greater sensitivity to unresolved disputes and historical grievances when forging new defence alignments. Risk reduction measures could include updating existing and historically relevant agreements, such as the Subregional Arms Control Agreement, to reflect contemporary security challenges, maintain regional military balance and ensure defence initiatives are not politicised or instrumentalised.  Crucially, defence cooperation should be explicitly tied into existing regional dialogues such as the Berlin Process, enabling further de-escalation, information sharing and confidence-building. Strengthening such dialogue formats can help prevent defence cooperation from unintentionally fuelling mistrust, rivalries or arms competition. The EU should reinforce its commitment to dialogue as an integral component of all new defence alignments in the region, linking strategic coordination with conflict prevention and trust-building; and ultimately ensuring that the EU’s approach strengthens cohesion and stability across the Western Balkans.

 A longer version of this article was published as part of the Horizon Europe InvigoratEU project’s Deliverable D8.4, ‘The Risks of a Reinvigorated EU-Western Balkans Defence Cooperation’, funded by the European Union with Grant Agreement number 101132124. It can be accessed here: https://zenodo.org/records/17579952 

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