September 11, commonly referred to as 9/11, denotes a series of four coordinated terrorist attacks by the Islamic extremist group al-Qaeda against the United States on the morning of Tuesday, September 11, 2001. The event is defined by the hijacking of four commercial airliners by 19 terrorists, which were then used as large-scale suicide weapons to strike prominent American landmarks, marking a pivotal moment in modern world history.
The attacks resulted in catastrophic damage and unprecedented loss of life. Two of the aircraft, American Airlines Flight 11 and United Airlines Flight 175, were crashed into the North and South Towers of the World Trade Center in New York City, leading to their collapse. A third aircraft, American Airlines Flight 77, struck the Pentagon in Arlington, Virginia. The fourth plane, United Airlines Flight 93, crashed into a field in Shanksville, Pennsylvania, after passengers and crew resisted the hijackers, thwarting a further attack on a target in Washington, D.C. The attacks killed 2,977 people, making it the deadliest terrorist incident in history.
The immediate aftermath of September 11 saw the U.S. launch the "War on Terror," leading to military interventions in Afghanistan and Iraq. Domestically, it prompted the creation of the Department of Homeland Security and the passage of new security legislation like the USA PATRIOT Act. Globally, the event fundamentally reshaped aviation security protocols and international counter-terrorism cooperation, and its effects on foreign policy, civil liberties, and international relations continue to be significant.
