On September 11, 2001, a series of coordinated terrorist attacks took place in the United States. Members of the extremist group Al-Qaeda hijacked four commercial airplanes. Two of these planes were flown into the World Trade Center towers in New York City, causing both towers to collapse. Another plane hit the Pentagon in Arlington, Virginia, while the fourth plane, United Airlines Flight 93, crashed in a field in Pennsylvania after passengers attempted to regain control from the hijackers. The attacks resulted in the deaths of nearly 3,000 people and caused significant changes in U.S. security policies. In response, the U.S. launched the War on Terror, which included military actions in Afghanistan to dismantle Al-Qaeda