How did the European Union expand into central and eastern Europe after the Cold War?

Following the end of the Cold War, many former communist countries in central and eastern Europe sought to join the European Union. This process of expansion presented significant challenges, primarily due to the relative lack of economic development in these nations, which threatened to hinder their full integration into EU institutions.1

To manage this transition, the EU considered a stratified system of integration, allowing for varying levels of participation in economic components, such as free trade areas versus the single currency. In preparation for these admissions, the EU implemented major institutional reforms through the Treaty of Nice, which adjusted the number of seats on the Commission and expanded the use of qualified majority voting to ensure the organization could function effectively with a larger membership.1

Despite concerns that rapid expansion might stifle consensus or inhibit foreign policy development, the EU admitted 10 countries in 2004—including the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, and Slovakia—followed by Bulgaria and Romania in 2007.1