In his book, “Black Flags: The Rise of ISIS” (now out in paperback), Pulitzer Prize-winning reporter Joby Warrick traces how the strain of militant Islam behind ISIS first arose in a remote Jordanian prison and spread with the unwitting aid of two American presidents. Drawing on high-level access to CIA and Jordanian sources, Warrick weaves moment-by-moment operational details with the perspectives of diplomats and spies, generals and heads of state, many of whom foresaw a menace worse than al Qaeda and tried desperately to stop it. Black Flags reveals the long arc of today’s most dangerous extremist threat.