On September 11, 2001, a major world event occurred when terrorists from the extremist group al-Qaeda carried out coordinated attacks on the United States. Four commercial airplanes were hijacked, two of which were flown into the Twin Towers of the World Trade Center in New York City, causing their collapse. A third plane struck the Pentagon, while the fourth plane, United Airlines Flight 93, crashed in Pennsylvania after passengers attempted to regain control. The attacks resulted in nearly 3,000 deaths and led to significant changes in U.S. domestic and foreign policy, including the War on Terror.