The attacks known as 9/11 took place on Sept. 11, 2001. This attack began with the hijacking of four commercial airplanes, followed by intended suicide attacks using the airplanes as weapons.
Hijackers flew two of the planes into the two towers of the World Trade Center in New York City. The third plane crashed into the Pentagon in Washington, D.C. The fourth plane crashed in a field in the state of Pennsylvania.
The death toll of these attacks was over 3,000, including over 400 fire fighters and police officers.
The 9/11 attacks started a military response from the United States government to end terrorism.