A major event that occurred in the United States on September 11, 2001, was a series of coordinated terrorist attacks orchestrated by the extremist group al-Qaeda. These attacks included the hijacking of four commercial airliners, two of which were flown into the Twin Towers of the World Trade Center in New York City, and another into the Pentagon in Arlington, Virginia. The attacks killed nearly 3,000 people and caused extensive destruction. The aftermath led to significant changes in U.S. domestic and foreign policy, including the War on Terror, increased security measures, and a heightened focus on national security.