In 1998/99 the European Union (EU) acknowledged a need for an autonomous military action force. In 2007 the European Battlegroups (EUBG) were ready for ‘rapid reaction’. Today, in the year of 2016, they have still never been deployed. – How come the EUBG still exist, even though they have never been used? By an approach of explaining outcome process tracing, this study address – How can we understand the persistence of EUBG within the European Union in terms of integration and disintegration of regional organisations? By the developed theoretical framework of Security Communities (SC), it is argued that the EU, as a ‘tight, pluralistic, mature security community’ possibly cannot revise the renowned EUBG; disintegrate the Union, due to external and internal pressures and integrated features. This is shown by a method of a triangulated approach of surveys, interviews and textual analysis. The research concludes that deep-rooted integration and strong loyalty prevent members, of a regional organisation, to express contingent dissatisfaction and/or leave cooperation.