When fighters from the Islamic State of Syria and al-Sham (ISIS) stole tens of millions of dollars from a bank in Mosul earlier this year, it wasn’t simply a startling symbol of the collapse of Baghdad’s control over Iraq’s second-largest city. The brazen theft was instead a stark illustration of one of the most alarming aspects of ISIS’s rise: the group’s growing ability to fund its own operations through bank heists, extortion, kidnappings, and other tactics more commonly associated with the mob than with violent Islamist extremists.