Countering Violent Extremism: A Realist Review for Assessing What Works, for Whom, in What Circumstances and How?

Europe is confronted with increased violent extremism, and the security threat is expected to rise further in the years to come. Within the EU, member states are especially concerned about jihadist terrorism. Particularly worrying is the phenomenon of foreign terrorist fighters, in which Europeans travel to and from conflict zones in Syria and Iraq. But jihadist terrorism is not the only issue. Right-wing and left-wing extremist violence and that of lone attackers also pose a threat (Europol, 2016; 2017).