Twenty years ago, four hijacked planes carried out attacks on the United States. Islamic extremists known as Al Qaeda were responsible for the attacks.
Two planes struck the twin towers of the World Trade Center in New York City, a third struck the Pentagon building in Washington, D.C., and a fourth crashed into a field in Pennsylvania. The 9/11 terrorist attacks killed more than 2,500 and left an indelible memory in the minds of Americans and the world. During the aftermath, volunteers from all over the country traveled to ground zero and surrounding areas to help in any way they could.