The downing of a Russian passenger plane over Egypt’s Sinai Peninsula last October, for which the Islamic State (also known as ISIS) claimed responsibility, may ultimately prove more consequential than thehorrific attacks in Paris and San Bernardino, California, that followed. Western security officials had long worried that their countries’ own citizens would conduct attacks after returning home from Iraq or Syria or strike out as “lone wolf” terrorists. But the Russian plane crash, which killed 224 people, was caused by a different beast: neither lone wolves nor ISIS itself but an ISIS affiliate that had pledged its loyalty to Abu Bakr al-Baghdadi, ISIS’ self-declared caliph. ISIS calls these groups wilayat, Arabic for “provinces.” (The term is borrowed from the seventh century, when the armies of Islam burst out of the Arabian Peninsula and established regional governors who ruled in the name of the caliph; ISIS also uses wilayat to refer to administrative divisions within Iraq and Syria.) If, as recent events suggest, ISIS far-flung provinces have begun closely aligning their actions with those of the group’s core leadership in Iraq and Syria, then ISIS geographic scope has expanded vastly.