In 1998 Osama bin Laden and his associates issued a fatwa— a judicial opinion interpreting Islamic religious and legal teachings. They asserted in the fatwa that it was the religious duty of Muslims to kill Americans in order to liberate Islam’s holy sites in Saudi Arabia. They also demanded that American military forces withdraw from all the “lands of Islam.” These prescriptions were justified using several passages from the Koran including the command to “fight the pagans all together as they fight you all together.” Bin Laden’s fatwa was acted on with deadly results on September 11, 2001, when members of his organization al-Qaeda carried out terrorist attacks that killed nearly three thousand people in New York City and Washington, D.C. These actions, and bin Laden’s words, are for some observers proof...