Editors' Note [Dec. 18, 2020]: The Times has published an Editors’ Note concluding that episodes featuring a central character in “Caliphate” did not meet our standards for accuracy. Read the full statement.

The war on terror has cost the U.S. billions and has been fought for nearly 20 years. Rukmini Callimachi, a foreign correspondent for The New York Times, asks, “Who are we really fighting?”