The fourth and final flight, United Airlines Flight 93, flew in the direction of the capital. Alerted to the previous attacks, the passengers retaliated in an attempt to take control of the aircraft, forcing the hijackers to crash the plane in a Stonycreek Township field, near Shanksville, at 10:03 a.m. Investigators determined that Flight 93’s target was either the United States Capitol or the White House.Within hours of the attacks, the Central Intelligence Agency had determined that al-Qaeda was responsible. The United States formally responded by launching the war on terror and invading Afghanistan to depose the Taliban, which rejected the conditions of U.S. terms to expel al-Qaeda from Afghanistan and extradite its leaders.
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.
