A year ago, the main fear was that foreign militants who had gone to fight with ISIS would be trained and then sent back to do damage in their own countries. However, there has been scarcely any of that.
In part, this is because, as Daniel Byman and Jeremy Shapiro have detailed in a Brookings Institution report, foreign fighters tend to be killed early (they are common picks for suicide missions); often become disillusioned, especially by in-fighting in the ranks; and do not receive much in the way of useful training for terrorist exercises back home. It might also be added that ISIS videos exultantly show foreign fighters burning their passports to demonstrate their terminal commitment to the cause — hardly a good idea if they want to return. In May 2015, an audio message apparently from the leader of ISIS exhorted Muslims either to join the ISIS ranks in the Middle East or to fight at home “wherever that may be.” There was nothing about training people to return home to wreak havoc.
More recently, the focus of fear has shifted from potential returnees to potential homegrown terrorists who might be inspired by ISIS’s propaganda or example. However, ISIS could continue to be an inspiration even if it was weakened or destroyed. And, as terrorism specialist Max Abrahms notes, “lone wolves have carried out just two of the 1,900 most deadly terrorist incidents over the last four decades.”