On Septmber 11, 2001, four airplanes were hijaked in a coordinated attack on the United States by Al-Qaeda, a terrorist organization based in Afghanistan. Two planes were crashed into the two World Train Center buildings, one crashed into the Pentagon, and one was heading to Washington D.C., but was taken down in a field in Pennsylvania.
9/11 caused $3 billion in damage. Two other buildings collapsed and four were severely damaged. Part of the pentagon collapsed.