Long before Osama bin Laden's death, al Qaeda had adapted itself to survive and operate without him, ensuring the threat his terror network poses will live well beyond his demise. Bin Laden spent the last decade on the run following the al Qaeda-mounted terrorist attacks in the U.S. on Sept. 11, 2001. But his fugitive status didn't render the network impotent. Instead, it forced an evolution: The original group splintered, popping up in new places with new leaders who, in addition to attempting high-profile attacks, encouraged their radicalized followers to strike on their own if the opportunity presented itself. Strong...