The major event in U.S. history that occurred on September 11, 2001, was a series of coordinated terrorist attacks by the Islamic extremist group al-Qaeda. Two commercial airplanes were hijacked and flown into the Twin Towers of the World Trade Center in New York City, resulting in their collapse, and a third plane struck the Pentagon. A fourth plane, United Airlines Flight 93, was intended to hit another target in Washington, D.C., but was thwarted by passengers. The attacks resulted in nearly 3,000 fatalities and led to widespread changes in U.S. domestic and foreign policy, including the initiation of the War on Terror.