If you are too young to remember September 11, 2001, it may be really challenging to imagine just how scary it was to be an American at that point in time.
On this very day in 2001, 19 terrorists hijacked four airplanes.
The hijackers then flew two of the airplanes into the World Trade Towers in New York City and one of the airplanes into the Pentagon in Arlington, Virginia.
In the fourth airplane, it is believed that passengers fought to take back control of the plane from the terrorists. That plane crashed into a field in Pennsylvania.
Many Americans died that day, a lot of families lost loved ones, and the rest of us sat by our televisions scared and shocked by what had just happened.