September 11 Attacks
On the morning of September 11, 2001, nineteen hijackers affiliated with the Islamist militant network al-Qaeda seized four commercial airliners in the United States and used them as weapons. The attacks killed nearly 3,000 people, the deadliest act of terrorism in modern history, and reshaped American foreign policy, global security practices, and international politics for decades.
Al-Qaeda was founded in the late 1980s by Osama bin Laden and others, many of whom had taken part in the Afghan resistance to the Soviet occupation. Bin Laden came to view the United States as the chief enemy of Muslims, citing its military presence in Saudi Arabia after the 1991 Gulf War, its support for Israel, and its influence in the Middle East. In 1996 and 1998 he issued public declarations of war against the United States, and the group carried out deadly attacks on American embassies in East Africa in 1998 and on the USS Cole in Yemen in 2000. Its leaders operated under the protection of the Taliban government in Afghanistan.
On the day itself, two planes were flown into the North and South Towers of the World Trade Center in New York, and both buildings collapsed within about two hours. A third plane struck the Pentagon in Virginia. The fourth, United Flight 93, crashed in a field in Pennsylvania after passengers attempted to retake the cockpit; it is widely believed the hijackers were heading for a target in Washington, D.C. Most of the dead were civilians, along with hundreds of firefighters, police officers, and other first responders. U.S. airspace was closed for the first time in history, and the nation watched the events unfold live on television.
The consequences were immense. Within weeks the United States launched military operations in Afghanistan to remove the Taliban and dismantle al-Qaeda, beginning what President George W. Bush called the War on Terror. Congress passed the USA PATRIOT Act, the Department of Homeland Security was created, and airport security was overhauled worldwide. NATO invoked its mutual defense clause for the first time. In 2003 the United States invaded Iraq, a decision that remains deeply controversial, as the claim that Iraq held weapons of mass destruction proved unfounded.
The legacy remains contested. Supporters of the response point to the absence of another attack on that scale in the U.S. and to the 2011 killing of bin Laden. Critics highlight the human and financial costs of long wars, surveillance expansion, detention practices at Guantánamo Bay, and rising suspicion toward Muslims. The United States withdrew from Afghanistan in 2021, and the Taliban quickly returned to power. The attacks continue to shape debates over security, liberty, and the use of military force.