Terrorists who were militants associated with the extremist Al-Qaeda group hijacked four American commercial planes on the morning of September 11, 2001, intending to use them in suicide attacks. In New York City, at 8:46 am, American Airlines Flight 11 was piloted by the hijackers into the North Tower of the World Trade Center, and United Airlines Flight 175 was flown into the South Tower at 9:03 am.

After the first plane hit, many people in the city and those watching news reports around the country thought a terrible accident had occurred; once the second plane hit, though, most considered it evident that it was a terrorist attack on the nation. At 9:37 am, American Airlines Flight 77 hit the southwest wall of the Pentagon near Washington, DC. The Federal Aviation Authority then ordered all planes in the air to land and all other flights grounded. Passengers on the fourth plane, United Airlines Flight 93, tried to overpower their hijackers; that plane crashed into a field near the small town of Shanksville in rural Pennsylvania, about 80 miles from Pittsburgh. At 9:59 am, the South Tower of the World Trade Center collapsed, followed by the North Tower at 10:28 due to damage to the buildings’ structural components from the subsequent fires.