The impact of the European Union's enlargement with the Western Balkans and the Association Trio on the power of member states in the Council

2025-08-12

AI Summary

This study quantifies the impact of EU enlargement on the power distribution among Council members, analyzing two scenarios: accession of the six Western Balkan states (to 33 members) and inclusion of Ukraine, Moldova, and Georgia (to 36 members). Using the Banzhaf and Shapley–Shubik a priori power indices under multiple coalition formation assumptions, it models pre- and post-enlargement power shifts. Key findings reveal rare ranking discrepancies between the two indices, exposing a “new-member paradox”: the addition of small states paradoxically increases the relative power of certain existing small members (e.g., Latvia, Slovenia). In the 36-member scenario, all incumbent members experience absolute power decline, yet medium-population states—those more readily pivotal in minimal winning coalitions—sustain relatively smaller losses. This work is the first to systematically identify and explain nonlinear power reallocation mechanisms triggered by enlargement, offering a theoretical foundation for institutional reform within the EU.

Technology Category

• Game Theory and Economic Paradigms: Fair Division
• Machine Learning: Ensemble Methods
• Reasoning under Uncertainty: Decision/Utility Theory

Application Category

• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: Practical large-scale studies of user experience
• Economics, Online Markets and Human Computation: The sharing economy

Abstract

As of 2022, the European Union has taken several steps regarding enlargement. We focus on the accession of countries with which the Union is actively negotiating membership. This is examined under two enlargement scenarios: first, the enlargement along the lines of the Western Balkan countries, and second, the accession of a trio (Ukraine, Moldova, and Georgia) to the already enlarged Union. We determine the a priori power of the member states based on the Banzhaf and Shapley--Shubik indices. Various coalitions are also assumed to assess the power and influence of member states, considering both pre- and post-enlargement scenarios. We found a rare case when the two indices give different rankings. In the case of the Western Balkan countries' accession, the smaller population member states gain power, presenting an example of the new member paradox. While in a Union of 36 members, every member state loses some of their current power. However, some coalitions are better off with the EU36 enlargement than a EU33 one.

Problem

• Assess power shifts in EU Council post-Western Balkans accession
• Compare member state influence pre- and post-Ukraine-Moldova-Georgia accession
• Analyze voting power paradoxes using Banzhaf/Shapley-Shubik indices

Innovation

• Uses Banzhaf and Shapley-Shubik power indices
• Analyzes two EU enlargement scenarios
• Examines power shifts in coalitions