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. Nineteen militants hijacked four commercial airliners. Two of the planes were flown into the North and South Towers of the World Trade Center complex in New York City. A third plane was crashed into the Pentagon in Arlington, Virginia, just outside Washington, D.C. The fourth plane, after passengers and crew attempted to retake control from the hijackers, crashed into a field in Shanksville, Pennsylvania.
The attacks resulted in 2,977 fatalities, excluding the 19 hijackers. The dead included 246 on the four planes, 2,606 in the World Trade Center and on the ground, and 125 at the Pentagon. The assault was the single deadliest terrorist attack in human history. The impact of the aircraft and the resulting fires caused the catastrophic structural failure of both 110-story towers of the World Trade Center, which collapsed completely, leading to the destruction of the surrounding complex. At the Pentagon, the impact caused the collapse of one section of the building. The fourth plane, United Airlines Flight 93, was believed to be targeting a significant federal building in Washington, D.C., such as the U.S. Capitol or the White House, but its mission was thwarted by the actions of those on board.
The immediate aftermath involved the grounding of all civilian air traffic in the U.S. and the initiation of extensive search and rescue operations. In the long term, the events profoundly reshaped American foreign policy and domestic security. The U.S. launched the "War on Terror," leading to the invasion of Afghanistan to dismantle al-Qaeda and overthrow the Taliban regime that had harbored them. Domestically, the U.S. government enacted significant security legislation, including the USA PATRIOT Act, and established the Department of Homeland Security to coordinate national security efforts, fundamentally altering protocols for air travel, surveillance, and counter-terrorism worldwide.
