The article discusses how the European Union has grown from 6 to 27 member states over the past 50 years, impacting politics, economics, and security. The researchers explore the mechanisms and patterns behind this enlargement, highlighting the importance of economic success and political interdependency. They also mention theories like neo-functionalism and liberal intergovernmentalism in understanding European integration. Despite the long history of EU enlargement, there is a lack of theoretical groundwork in this area.