September 11 attacks: A day that changed the world

On Sept. 11, 2001, the United States was attacked in a series of coordinated terrorist attacks that killed nearly 3,000 people and changed the course of modern history.

Nineteen al-Qaida terrorists hijacked four commercial passenger planes. Two were flown into the World Trade Center towers in New York City, while a third struck the Pentagon in Arlington, Va.

The fourth aircraft, United Airlines Flight 93, crashed into a field near Shanksville, Pa., after passengers and crew attempted to regain control of the plane.

The attacks brought down both World Trade Center towers and caused extensive damage to the surrounding area. The Pentagon was also severely damaged.

The attacks prompted major changes to security and foreign policy in the United States and led to the U.S.-led war in Afghanistan against the Taliban and al-Qaida.

The events also had a profound impact in Canada. Under Operation Yellow Ribbon, dozens of international flights were diverted to Canadian airports after U.S. airspace was closed. Among the communities that welcomed stranded passengers was Gander, N.L., where thousands of people were cared for by local residents.

Twenty-five years later, the attacks continue to be remembered through ceremonies and memorials in the United States, Canada and around the world.