EU enlargement could address collective action problems and stabilise its neighbourhood, but stalled accession processes may make full membership unlikely. Maria Giulia Amadio Viceré and Matteo Bonomi suggest that partial integration — engaging candidate countries in EU policies without membership — will remain the EU's main strategy for managing internal and regional crises
In response to Russia’s full-scale invasion of Ukraine, the EU extended its enlargement policy to include post-Soviet states, and renewed its engagement with the Western Balkans. The shift aimed to secure these countries' alignment with the EU’s response to the war and prevent their drift toward rival international actors. However, while enlargement could address collective action problems and stabilise the EU’s neighbourhood, conditions supporting this renewed commitment are rapidly diminishing.
The unpredictability of the war’s trajectory — compounded by uncertainty over security guarantees for Ukraine and the likely erratic policies of a new Trump administration — adds to the volatility. At the same time, domestic reform challenges in candidate countries, and persistent divisions among EU member states over expansion, continue to hinder the enlargement process.
Domestic reform challenges in candidate countries, and persistent divisions among EU member states over expansion, continue to hinder the enlargement process
Against this backdrop, the EU is likely to rely on integrating candidate countries into its policies without offering clear timelines or guarantees of membership. This approach allows the EU to maintain regional cooperation while avoiding the contentious political hurdles of full accession.
The EU’s approach to the Western Balkans offers valuable insights into this strategy. Despite strong political and economic incentives for these countries to join the EU, enlargement has largely stalled since Croatia’s accession in 2013, due to divisions among member states. Over the past decade, however, Western Balkan countries have played an active role in crisis management efforts and fed into a series of EU policies.
These countries have joined the EU in addressing critical challenges, such as managing migratory flows and mitigating the health and socio-economic impacts of the Covid-19 pandemic. This highlights how integration short of membership can maintain regional cooperation and involve candidate countries in addressing shared challenges, even when the path to full membership remains uncertain.
The EU's relationship with the Western Balkans shows how integration short of full membership can maintain regional cooperation and address shared challenges
The unfolding of what might be understood as external differentiated cooperation in EU interactions with the Western Balkans has served as a compromise route for EU actors to ensure the involvement of Western Balkan countries in the EU response to crises that might affect the EU itself, and the countries that surround it.
External differentiated cooperation is a mode of governance based on consensus-seeking practices and on non-homogenous voluntary policy coordination between the EU and enlargement countries. This mode of governance may include enlargement countries’ participation in EU policy sectors normally reserved for EU member states through their informal participation in collective EU institutions such as EU leaders’ summits and the Council of the EU, their establishment of new agreements with the EU, and their adoption of EU rules, as well as their involvement in EU agencies, operational bodies and programmes. In essence, through external differentiated cooperation, the EU has adjusted the boundaries set on enlargement countries’ participation in its policies without formally revising its approach to them.
The Russia-Ukraine war has amplified the bargaining power of enlargement countries while heightening the EU's reliance on them. In response, the EU has offered membership prospects while simultaneously supporting the integration of these countries into its policies — short of accession. Notably, the European Commission is considering 'pre-enlargement policy reviews' to support the gradual integration of candidate countries into selected EU policies before full membership. Such reviews couple with the EU's establishment of a New Growth Plan for the Western Balkans aimed at enhancing these countries' integration into the EU single market. They also coincide with measures integrating Ukraine into strategic EU policy sectors within the framework of the Ukraine Facility.
The Russia-Ukraine war has amplified the bargaining power of enlargement countries, while heightening the EU's reliance on them
Granted, the gradual integration of these countries may foster their economic and political convergence with the EU, facilitating their future accession. As the war in Ukraine is likely to turn into a frozen conflict, and enlargement continues to be out of reach, however, external differentiated cooperation may once again become the dominant EU strategy in its approach to enlargement countries. Enlargement countries, in turn, are likely to accept being integrated into EU policies through forms of differentiated cooperation because of their increased dependence on the EU. Â
Blending the promise of full accession with partial integration of enlargement countries may serve as an efficient strategy for the EU in the short to medium term. Such a blend may ease EU management of internal and regional crises, and foster the stability of its neighbourhood against the backdrop of an international arena marred by security predicaments. In the long term, however, the employment of differentiated cooperation may be counterproductive.
If not channelled institutionally into an explicit path towards full membership, and accompanied by clearly defined strategic objectives with a coherent approach, differentiated cooperation may exacerbate instability and erode trust between the EU and these countries. As such, it may come with tangible risks for EU interactions with candidate countries, complicating their eventual integration.  Â
