Nearly 3,000 people were killed during the terrorist attack on 9/11.
People believe that Osama Bin Laden -who is in charge of Al-Qaeda - was the main man behind this attack.
The U.S. has spent over 1.5 trillion on war ever since the 9/11 attack.
The U.S. and the British in Afghanistan was in late 2001.
The terrorist hijacked four airplanes and flew the into the Twin Towers.
This is the reason why the war started because of the terrorist attack.