Drivers of differentiated enlargement to the Western Balkans

Differentiated integration is widely presented as a solution for stagnation of enlargement by offering an alternative pathway towards EU membership. Simultaneously, theoretical literature regards it as a suboptimal outcome of European Integration, when low interdependence or high politicization prevent full integration. In the context of the Western Balkans, explanations bifurcate between a politicization-focused and an interdependence-focused under-standing. While the former highlights the impact of ideational heterogeneity on differentiation through the mechanism of politicization, the latter emphasizes asymmetrical interdependence between the EU and the Western Balkans as a key driver of differentiation. To further explore the theoretical understanding of differentiated integration in the Western Balkans, this paper presents and empirically tests four potential causal mechanism lying behind the assumed causal relationship between key drivers of differentiation – ideational heterogeneity and asymmetric interdependence – and differentiated integration through a comparative case study of Montenegro, North Macedonia and Serbia. Results provide further evidence for the assumed causal impact of both ideational heterogeneity and asymmetric interdependence on differentiated integration. Furthermore, evidence is found for the opposite causal direction, showing that differentiation can reinforce and strengthen its drivers. Differences in the relative impact of the concrete driver of differentiation shows to determine future integration trajectories. While interdependence-based differentiation in Montenegro acts as a facilitator of integration, politicization-based differentiation in North Macedonia and Serbia tends to have a degressive political effect by fostering ideational heterogeneity between the candidate states and the EU. Capturing both the multi-causal nature of differentiation and its divergent impact in the region, the paper concludes by conceptualizing differentiated enlargement.