United States
On September 11, 2001, nineteen al-Qaeda hijackers seized four commercial airplanes and carried out coordinated suicide attacks against the United States. Two planes were flown into the twin towers of the World Trade Center in New York City, causing both towers to collapse.
A third plane struck the Pentagon near Washington, D.C., and a fourth crashed in a Pennsylvania field after passengers attempted to overpower the hijackers. Nearly 3,000 people were killed, including civilians, first responders, and military personnel. The attacks led to sweeping changes in U.S. foreign and domestic policy, including the wars in Afghanistan and Iraq and the creation of the Department of Homeland Security and the USA PATRIOT Act.