The purpose of this study is to identify the possible changes in the Islamic State's (IS) strategy after the collapse of its strongholds in the Middle East, and to explore possible countermeasures that European countries might implement to mitigate the future threat. This study discusses new security challenges posed by the IS within Europe. This study describes the IS`s most likely course of action in Europe after the loss of its main territory in the Middle East using Joint Intelligence Preparation of the Operational Environment, develops a possible operational approach through Army Design Methodology, and recommends countermeasures to mitigate the threat. It is expected that the IS will increase its use of foreign fighters for conducting attacks and recruitment, and that the EU can mitigate those actions through legislative, institutional and infrastructural countermeasures. Effective counter-terrorism in Europe depends on the offensive development and coordinated implementation of legislative, institutional, and infrastructure development focused countermeasures to achieve a long-term solution.