The Jihadist Returnee Threat: Just How Dangerous?

On 24 May 2014, Mehdi Nemmouche opened fire and killed four people at the Jewish Museum of Belgium in Brussels. Nemmouche was a French citizen who had fought in Syria, and his attack appeared to fulfill the biggest fear of U.S. and European counterterrorism officials: that the Syrian war would prove to be an incubator of terrorism on the scale of Afghanistan before September 11 or worse. A few months later, Moner Mohammad Abusalha raised alarms in the United States by becoming the first American to conduct a suicide attack in Syria. Most dramatic and deadly of all, on 13 November 2015, teams of attackers linked to the Islamic State killed 130 people in Paris, and several foreign fighters—including the probable mastermind—were among their ranks. Yet not every war in the Muslim world that draws Western recruits produces international terrorism when the foreign fighters return home. Indeed, some, such as those in Somalia and Mali, led to little terrorism “bleedout”—in contrast to Afghanistan, which spawned numerous terrorist attacks.