What happened on September 11, 2001?
On September 11, 2001, hijacked airliners struck the World Trade Center and the Pentagon, killing 2,977 people — and the world that followed was not the world that came before.
Last updated: October 2026
It began as a clear Tuesday morning in New York. It ended with two of the tallest towers on earth reduced to dust, a burning gash in the Pentagon, a field in Pennsylvania — and 2,977 dead. Nothing about the twenty-first century would be negotiated afterward; everything would be shaped by it.
Tuesday, 11 September 2001, began as an ordinary working morning in the eastern United States. At 8:46 a.m. local time, American Airlines Flight 11, which had been hijacked after taking off from Boston bound for Los Angeles, struck the North Tower of the World Trade Center in New York. Seventeen minutes later, at 9:03 a.m., United Airlines Flight 175, also hijacked after leaving Boston, struck the South Tower. Both towers were 110 storeys tall, among the tallest buildings on earth, and both were full of people starting their working day.
At 9:37 a.m., American Airlines Flight 77, hijacked after departing Washington Dulles for Los Angeles, struck the Pentagon, the headquarters of the United States Department of Defense, just outside Washington. A fourth hijacked aircraft, United Airlines Flight 93, bound from Newark to San Francisco, crashed into a field near Shanksville, Pennsylvania, at about 10:03 a.m. Accounts reconstructed from cockpit recordings and telephone calls indicate that passengers on board fought to regain control of the aircraft, and investigators believe the hijackers brought the plane down rather than surrender it.
Both towers of the World Trade Center collapsed: the South Tower at 9:59 a.m., the North Tower at 10:28 a.m. The collapses, the fires, and the debris destroyed or badly damaged surrounding buildings across Lower Manhattan. The United States Federal Aviation Administration grounded all civilian air traffic, the first time such an order had been given, and airspace over the country was closed. In the evening, President George W. Bush addressed the nation from the White House, promising that the attacks would be answered.
The National Commission on Terrorist Attacks Upon the United States, known as the 9/11 Commission, concluded in its 2004 report that the attacks were planned and carried out by al-Qaeda, the militant network led by Osama bin Laden, and that nineteen hijackers took part: five on each of three aircraft, and four on United Flight 93. According to the Commission, the operation was conceived by Khalid Sheikh Mohammed, who later said he had proposed the idea to bin Laden. Bin Laden publicly claimed responsibility for the attacks in 2004.
Official counts put the number of people killed at 2,977, not including the hijackers. The victims included office workers, firefighters, police officers, paramedics, military personnel at the Pentagon, airline crews, and passengers. More than ninety countries lost citizens in the attacks. In the years that followed, thousands more rescue and recovery workers and residents reported illnesses that researchers have linked to dust and smoke from the site, and a federal compensation fund was created for victims and responders.
Within weeks, the United States led a military campaign in Afghanistan, beginning on 7 October 2001, aimed at removing the Taliban government, which had sheltered al-Qaeda, and destroying the network's bases there. The Taliban government fell quickly, but the war that followed lasted two decades, ending with the withdrawal of American forces in 2021. In 2003, a United States-led coalition invaded Iraq, a decision the American administration justified on grounds that included alleged Iraqi weapons of mass destruction, which were not found. Both wars, and the wider campaign described by the Bush administration as a war on terror, remain the subject of intense historical debate.
At home, Congress passed the USA PATRIOT Act in October 2001, expanding surveillance and law-enforcement powers. In 2002, Congress created the Department of Homeland Security, which began operating in 2003, bringing together agencies responsible for borders, transport security, emergency response, and related work. Airport security was federalised under the new Transportation Security Administration. The North Atlantic Treaty Organization invoked its collective-defence clause, Article 5, for the first and so far only time, and many countries tightened their own security laws.
The site of the World Trade Center in New York, known as Ground Zero, was cleared over months of painstaking recovery work. A memorial opened there in September 2011, on the tenth anniversary, with two reflecting pools set in the footprints of the Twin Towers and the names of the victims inscribed on bronze parapets. A museum opened on the site in 2014. Each year on 11 September, the names of the dead are read aloud at the memorial, and two beams of light, the Tribute in Light, rise over Lower Manhattan.
At the Pentagon, a memorial of 184 benches, one for each victim killed there, opened in 2008. In Pennsylvania, a national memorial marks the crash site of Flight 93, where a wall of names and a tower of wind chimes honour the passengers and crew. In 2011, United States forces killed Osama bin Laden during a raid in Abbottabad, Pakistan. The date has since become a fixed point in public memory: a day of mourning, of debate about security and liberty, and of argument over what the twenty-first century became.
- The 9/11 Commission Report, National Commission on Terrorist Attacks Upon the United States (2004).
- National September 11 Memorial & Museum, New York.
- National Institute of Standards and Technology, reports on the collapse of the World Trade Center towers.
- United States Department of State, Office of the Historian.
- Encyclopaedia Britannica, entry on the September 11 attacks.