The September 11, 2001 attacks were orchestrated by the Islamist extremist group al-Qaeda. The attacks were masterminded by al-Qaeda leader Osama bin Laden, with the key operational planning done by Khalid Sheikh Mohammed. Mohammed came up with the plan of hijacking planes and crashing them into targets in the United States. Nineteen militants associated with al-Qaeda carried out the attacks, most of whom were Saudi nationals. The hijackers were divided into teams, with some receiving commercial flight training within the U.S. The attacks targeted the World Trade Center in New York and the Pentagon in Washington, D.C. Osama bin Laden was killed by U.S. forces in 2011, and Khalid Sheikh Mohammed was captured in 2003.
The attacks had profound impacts, leading the U.S. to declare a "war on terrorism," invade Afghanistan to dismantle al-Qaeda, and increase domestic security measures, including the creation of the Department of Homeland Security.
