An aerial observation drone records a Combined Joint Task Force - Operation Inherent Resolve double airstrike on an ISIS tunnel system in the vicinity of Mosul, Iraq on or around Dec. 13, 2020.

While the Islamic State can no longer operate as an overt militant force, sleeper cells still operate in darkness and on the fringes of Iraqi society. Baghdadi may have been killed and Mosul liberated, but the hardline Islamist ideology lives on, waiting for the opportunity to resurge.