Planning of the September 11 attacks

On September 11, 2001, 19 Arab-Muslim hijackers took control of four commercial aircraft and used them as suicide weapons in a series of four coordinated acts of terrorism to strike the World Trade Center in New York City, the Pentagon in Arlington County, Virginia, and an additional target in Washington, D.C. Two aircraft hit the World Trade Center while the third hit the Pentagon. However, one plane never arrived at its target; it crashed in a field in Pennsylvania because the passengers fought back. The intended target is believed to have been either the United States Capitol or the White House. As a result, 2,977 victims were killed, making it the most deadly terrorist attack on U.S. soil; also the deadliest foreign attack on U.S. soil, exceeding Japan's surprise attack on Pearl Harbor in Honolulu, Hawaii, on December 7, 1941, which killed 2,403 victims. It was carefully planned by al-Qaeda, who sent 19 terrorists to take over Boeing 757 and Boeing 767 aircraft, operated by American Airlines and United Airlines.

Al-Qaeda's origins date back to 1979 when the Soviet Union invaded Afghanistan. Soon after the invasion, Osama bin Laden traveled to Afghanistan and helped organize Arab mujahadeen. Together with Abdullah Azzam, a Palestinian-Jordanian who influenced bin Laden, they formed Maktab al-Khidamat (MAK) in 1984, to provide support for Arab mujahadeen who came to join the jihad in Afghanistan.