The war against ISIS has been going since the group seized large swaths of territory in Iraq and Syria in mid-2014.

Backed by U.S.-led coalition airpower, Iraqi security forces retook Mosul in July 2017, and the SDF captured Raqqa in October 2017.

Several thousand ISIS fighters surrendered to the SDF during its 2018-2019 offensive

Shortly before the fall of Baghouz, General Joseph Votel, the outgoing commander of U.S. Central Command, warned Congress that ISIS made a “calculated decision to preserve the safety of their families and preservation of their capabilities by taking their chances in camps for internally displaced persons, and going to ground in remote areas and waiting for the right time to resurge.”