The fall of former President Bashar Assad‘s regime in Syria creates a new wrinkle in a long-standing U.S. security concern: the thousands of detained Islamic State fighters held in prisons controlled by the Syrian Democratic Forces.

Several current and former defense officials warned prior to the fall of Assad that the prisons, along with the refugee camps filled with the wives and children of those fighters, could represent a new generation of ISIS fighters if the West didn’t act, in particular by repatriating and rehabilitating those people.