On September 11, 2001, a series of coordinated terrorist attacks were carried out on the United States by the extremist group Al-Qaeda. The attacks involved four hijacked commercial airplanes, two of which were flown into the twin towers of the World Trade Center in New York City, causing both towers to collapse. Another plane was flown into the Pentagon building in Virginia, causing significant damage, while the fourth plane crashed into a field in Pennsylvania after passengers attempted to overcome the hijackers.

The attacks resulted in the deaths of nearly 3,000 people, including passengers and crew on the planes, workers in the World Trade Center towers, and first responders who were attempting to rescue people from the buildings. It was one of the deadliest terrorist attacks in US history and a turning point in global politics.

The 9/11 attacks led to significant changes in US policy, including the establishment of the Department of Homeland Security, the creation of the Transportation Security Administration, and the launch of the War on Terror, which included the invasions of Afghanistan and, later, Iraq. The attacks also had a profound impact on global attitudes toward terrorism, national security, and civil liberties.

In 2003, the United States led a coalition of countries, including the United Kingdom, in an invasion of Iraq.