At least that's what we think...

One of the biggest terrorist attacks on the U.S was 9/11.

On a clear, sunny late summer day in September 2001, Al Qaeda terrorists aboard three hijacked passenger planes carried out coordinated suicide attacks against the World Trade Center in New York City and the Pentagon in Washington, D.C., killing everyone on board the planes and nearly 3,000 people on the ground. A fourth plane crashed into a Pennsylvania field, killing all on board, after passengers and crew attempted to wrest control from the hijackers.