The September 11 Attacks
On the morning of September 11, 2001, nineteen hijackers affiliated with al-Qaeda seized four commercial airliners and carried out coordinated suicide attacks across the eastern United States. Two planes were flown into the Twin Towers of the World Trade Center in New York City, causing both 110-story towers to collapse; one was flown into the Pentagon in Arlington, Virginia; and a fourth, United Airlines Flight 93, crashed into a field near Shanksville, Pennsylvania after passengers attempted to overpower the hijackers. 2,977 people were killed — the deadliest foreign attack on American soil in history.
The FBI launched PENTTBOM, the largest criminal investigation in American history, identifying all nineteen hijackers within days from passenger manifests, surveillance footage, and physical evidence. The investigation established that the plot had been organized by Osama bin Laden and senior al-Qaeda leadership, coordinated through cells in Hamburg and the United States over several years. The 9/11 Commission, established in 2002 and reporting in 2004, documented the planning, financing, and execution of the attacks in extraordinary detail, as well as the intelligence failures that allowed it to succeed.
The attacks triggered the United States' invasion of Afghanistan in October 2001 to destroy al-Qaeda's sanctuary under the Taliban government, as well as the 2003 invasion of Iraq under the separate and disputed claim that Iraq possessed weapons of mass destruction. The broader "War on Terror" reshaped American foreign policy, domestic surveillance law, airport security, immigration procedures, and civil liberties for a generation. Osama bin Laden evaded capture for nearly a decade before being killed by U.S. Navy SEALs in Abbottabad, Pakistan on May 2, 2011.
September 11 remains the defining event of early twenty-first century American history, a wound whose consequences — in foreign policy, civil liberties, national security architecture, and cultural psychology — are still being felt and contested. The 9/11 Memorial and Museum in New York City commemorates the victims, and the rebuilt One World Trade Center stands as the tallest building in the Western Hemisphere. Five Guantánamo Bay detainees including Khalid Sheikh Mohammed, identified as the operational mastermind, remained in pretrial military commission proceedings as of 2025 — more than twenty years after the attacks.