The September 11 attacks, often called 9/11, were a series of four coordinated terrorist attacks by the Islamist terrorist group al-Qaeda against the United States on September 11, 2001. On that morning, 19 terrorists hijacked four commercial airliners. Two of the planes were flown into the Twin Towers of the World Trade Center in New York City, a third plane hit the Pentagon in Arlington County, Virginia, just outside of Washington, D.C., and the fourth plane crashed in a field in rural Pennsylvania after some of the passengers and crew attempted to regain control of the plane.
The attacks killed 2,977 people from 90 nations. The collapse of the Twin Towers destroyed the remaining five structures in the World Trade Center complex. The FBI's investigation of the attacks was code-named "PENTTBOM". It was the largest case ever handled by the FBI. In the immediate aftermath, the FBI worked to identify the attackers and prevent any future attacks. The events of 9/11 led to the U.S. launching its "war on terror".
