On September 11, 2001, a series of four coordinated terrorist attacks were carried out by the Islamic extremist group al-Qaeda against the United States. The attacks resulted in 2,977 fatalities, over 25,000 injuries, and substantial long-term health consequences, in addition to at least $10 billion in infrastructure and property damage. It remains the deadliest terrorist attack in world history.
The attacks began when 19 al-Qaeda terrorists hijacked four commercial airliners. American Airlines Flight 11 and United Airlines Flight 175 were intentionally crashed into the North and South Towers, respectively, of the World Trade Center complex in New York City; both 110-story towers collapsed within an hour and forty-two minutes. A third plane, American Airlines Flight 77, was crashed into the Pentagon in Arlington, Virginia. The fourth plane, United Airlines Flight 93, was initially targeted for Washington, D.C., but crashed into a field in Shanksville, Pennsylvania, after passengers and crew attempted to regain control from the hijackers.
The immediate consequence of these events was the initiation of the "War on Terror," leading to the U.S. invasion of Afghanistan to depose the Taliban, which had harbored al-Qaeda. Domestically, the attacks prompted the creation of the Department of Homeland Security and ushered in sweeping changes to national security and surveillance legislation, such as the USA PATRIOT Act. Globally, airport security protocols were fundamentally and permanently altered, and international counter-terrorism cooperation was significantly intensified, reshaping foreign policy and geopolitical alliances for decades.
