On September 11, 2001, 19 militants associated with the Islamic extremist group al Qaeda hijacked four airplanes and carried out suicide attacks against targets in the United States. Two of the planes were flown into the twin towers of the World Trade Center in New York City, a third plane hit the Pentagon just outside Washington, D.C., and the fourth plane crashed in a field in Shanksville, Pennsylvania. Almost 3,000 people were killed during the 9/11 terrorist attacks, which triggered major U.S. initiatives to combat terrorism and defined the presidency of George W. Bush.
On September 11, 2012 U.S. Ambassador to Libya J. Christopher Stevens, U.S. Foreign Service Information Management Officer Sean Smith, and CIA contractors and former Navy SEALs Glen “Bub” Doherty and Tyrone Woods were killed when the compound was ambushed in a coordinated attack by the Islamic militant group Ansar al-Sharia.