European Union and the fight against terrorism: a differentiated integration theory perspective

Although many EU member states experienced large scale terrorist attacks and both national and EU policymakers have repeatedly acknowledged the need to tackle the apparent contradiction between borderless terrorism and national counterterrorism measures, a genuine supranational EU counterterrorism response has not emerged thus far. In this article, we explore why this has been the case. Via a set of proxy indicators, we operationalize and test three key variables derived from differentiated integration theory, which suggests that the lack of horizontal and vertical integration in the EU's counterterrorism policy ought to be the result of high and asymmetric politicization, asymmetrical interdependence, and little preference convergence across EU member states. Our findings indicate that although all of these variables did influence integration in the first fifteen years of EU counterterrorism policy (2001-2016), only one variable (interdependence) acted exactly as expected by differentiated integration theory.