The U.S.’s invocation of Article 5 of the North Atlantic Treaty—its only usage to date—called upon allies to fight al-Qaeda. As U.S. and NATO invasion forces swept through Afghanistan, al-Qaeda leader Osama bin Laden disappeared into the White Mountains, eluding captivity by western forces. Although bin Laden initially denied any involvement, in 2004 he formally claimed responsibility for the attacks. Al-Qaeda’s cited motivations included U.S. support of Israel, the presence of U.S. military bases in Saudi Arabia and sanctions against Iraq.