The September 11 attacks occurred in the United States in the year 2001. On the morning of September 11, terrorists from the extremist group al-Qaeda hijacked four commercial airplanes. Two of these planes were flown into the Twin Towers of the World Trade Center in New York City, causing them to collapse. Another plane struck the Pentagon in Arlington, Virginia, while the fourth flight, United Airlines Flight 93, was thwarted by passengers and crashed in a field in Pennsylvania. Nearly 3,000 people were killed in these coordinated attacks, profoundly impacting U.S. domestic and foreign policy, leading to significant changes in security measures and the initiation of the War on Terror.