More than 30,000 foreign fighters from 100 countries have entered ongoing conflicts in Syria and Iraq since 2011. While the flow of these fighters has decreased dramatically over the past twelve months, two important concerns remain regarding foreign fighters. First, foreign fighters could radicalize rebel groups causing an escalation of violence in conflicts, lengthening their duration, and/or reducing opportunities for their resolution. Second, upon the conclusion of their participation in foreign conflicts, these fighters could try to return to their home countries and carry out deadly attacks. In two articles at Research & Politics and Journal of Conflict Resolution, we suggest that both of these concerns are easily exaggerated.
Previous studies present divided evidence as to whether foreign fighters aid or undermine the rebels that they join. On the one hand, data summarizing foreign fighter participation across the period 1900 to 2006 suggest that conflicts involving foreign fighters were more likely, on average, to conclude with insurgent victory than with government victory. On the other hand, in Chechnya, the arrival of foreign fighters perverted the goals of local rebels, negatively affecting their resource and recruitment bases and losing them support within local populations.