On this day 18 years ago, America was changed.
Almost 3,000 Americans lost their lives in the worst terrorist attack in U.S. history.
19 Al Qaeda terrorists hijacked four airplanes crashing two into the twin towers at the World Trade Center in New York City, one into The Pentagon in Washington, D.C., and the other crashed in Shanksville, PA after the passengers fought to take the plane back from the hijackers.
Americans joined together on September 11, 2001, to mourn the loss of thousands, unite in patriotism, and make a vow to never forget.
The attacks triggered major efforts to combat terrorism.
For more about the 9/11 attacks, check out this article from History.com.