On a cold and blustery evening in December 1989, Huthaifa Azzam, the teenage son of the legendary Jordanian-Palestinian mujahideen leader Sheikh Abdullah Azzam, went to the airport in Peshawar, Pakistan, to welcome a group of young men. All were new recruits, largely from Jordan, and they had come to fight in a fratricidal civil war in neighboring Afghanistan—an outgrowth of the CIA-financed jihad of the 1980s against the Soviet occupation there. The men were scruffy, Huthaifa mused as he greeted them, and seemed hardly in battle-ready form. Some had just been released from prison; others were professors and sheikhs. None...