Today marks 25 years since the September 11, 2001, terrorist attacks that killed nearly 3,000 people and changed the United States forever.

Nineteen al-Qaeda terrorists hijacked four commercial airplanes, crashing two into New York’s World Trade Center and one into the Pentagon.

Passengers and crew members on United Airlines Flight 93 fought back against the hijackers before the plane crashed in a Pennsylvania field.

The attacks led to major changes in U.S. national security and foreign policy, including the war in Afghanistan, Scripps News has reported.

The anniversary is being commemorated with ceremonies and events at all three attack sites and across the country.