On September 11, 2001, a series of coordinated terrorist attacks were carried out by the extremist group Al-Qaeda in the United States. Four commercial airplanes were hijacked, with two crashing into the World Trade Center towers in New York City, one into the Pentagon in Arlington, Virginia, and the fourth, United Airlines Flight 93, crashing in a field in Pennsylvania after passengers attempted to regain control. The attacks resulted in the deaths of nearly 3,000 people and caused significant destruction. In response, the U.S. government initiated the War on Terror, leading to military actions in Afghanistan and changes in national security policies.