1. September 11, 2001 Attacks (9/11)
Often called "9/11," these were four coordinated terrorist attacks by al-Qaeda against the U.S..
Casualties: 2,977 victims were killed.
Targets:
New York City: Two planes struck the Twin Towers of the World Trade Center, causing both to collapse.
Arlington, VA: A third plane hit the Pentagon, the headquarters of the U.S. Department of Defense.
Shanksville, PA: A fourth plane (Flight 93) crashed in a field after passengers fought back; it was likely headed for the U.S. Capitol or the White House.
Impact: The attacks led to the "War on Terror," the invasion of Afghanistan, and the creation of the Department of Homeland Security.
