September 11 attacks

Overview

The September 11 attacks were coordinated terrorist hijackings carried out by al-Qaeda in the United States on September 11, 2001. Nineteen operatives seized four commercial passenger aircraft. They flew two into the twin towers of the World Trade Center in New York City and one into the Pentagon outside Washington, D.C. The fourth, United Airlines Flight 93, crashed near Shanksville, Pennsylvania, after passengers and crew resisted the hijackers. The attacks killed 2,977 people apart from the 19 perpetrators. Their targets included central symbols of American economic and military power, but most of those killed were civilians going about ordinary work and travel.

Al-Qaeda’s leader, Osama bin Laden, directed the organization responsible for the operation. Ayman al-Zawahiri was among its senior leaders and masterminds, while Ramzi bin al-Shibh helped coordinate logistics. The attacks brought an immediate American military campaign against al-Qaeda and the Taliban government that sheltered bin Laden in Afghanistan. They also prompted international efforts to freeze terrorist assets, reorganize intelligence work and prevent further attacks. Investigations continued for years, including inquiries into possible assistance to individual hijackers from people with Saudi government connections. Those inquiries did not establish that the Saudi state directed the operation.

September 11 became a defining event in American public life and international security. Its anniversary remains an occasion for remembrance of those killed and for examination of the decisions made before and after the attacks. Al-Qaeda has also repeatedly used the date to glorify its operatives and recruit supporters. That propaganda has circulated alongside false conspiracy theories attempting to shift responsibility from the organization that carried out the hijackings.

Background

Al-Qaeda was founded in March 1988. It developed a transnational network of operatives, training facilities and supporters, first around Afghanistan and Pakistan and later in Sudan. After May 1996, its leadership relocated to Afghanistan, where the Taliban government gave bin Laden sanctuary. Its camps trained militants from multiple countries, and its leaders gained room to organize attacks beyond Afghanistan. Before September 11, al-Qaeda operatives bombed United States embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania, in 1998. The organization also attacked the USS Cole in Aden, Yemen, in 2000. These operations preceded its plan to strike targets inside the United States.

The September 11 plot required hijackers, travel arrangements and coordination across several countries. Fifteen of the 19 hijackers were nationals of Saudi Arabia; two were citizens of the United Arab Emirates. Dubai served as a transit point for some participants. Khalid Sheikh Mohammed, who masterminded the aircraft plot, had previously lived and worked in Qatar from 1993 to 1996. These connections describe parts of the network’s movements and origins; nationality and transit alone do not assign responsibility to a government. The operation itself was planned and carried out by al-Qaeda.

United States agencies received warnings of a major terrorist threat before the attacks. In August 2001, Mossad warned the FBI and CIA that terrorists were entering the United States and planning a major assault. The warning did not prevent the hijackings. Subsequent reviews of intelligence and law enforcement practices examined how information about al-Qaeda and potential operatives was collected, shared and acted upon. September 11 exposed the difficulty of detecting a coordinated operation assembled through international travel, domestic preparation and a network already responsible for lethal attacks abroad.

Al-Qaeda presented its violence in religious and political terms. Jihad means struggle or effort; the organization advocated armed jihad and used terrorism as a tactic. Its stated hostility toward the United States and its allies formed part of its program, but that program did not speak for Muslims as a whole. The distinction matters when describing the perpetrators: the nineteen men were al-Qaeda operatives who chose to carry out mass murder. Their conduct cannot be inferred from the religion, nationality or ordinary demeanor of other people.

The attack

On the morning of September 11, the nineteen hijackers boarded four passenger flights departing from airports in the northeastern United States. They seized the aircraft after takeoff and turned them toward selected targets. American Airlines Flight 11 struck the North Tower of the World Trade Center. United Airlines Flight 175 struck the South Tower as the emergency response to the first impact was under way. Fires and structural damage caused both towers to collapse. The destruction killed people inside the buildings, aboard the aircraft and in the surrounding area, including responders who entered the complex to rescue others.

American Airlines Flight 77 struck the Pentagon in Arlington County, Virginia. The attack killed passengers and crew aboard the aircraft and people working inside the building. As the headquarters of the United States Department of Defense, the Pentagon was a deliberate military symbol. The World Trade Center, a major office and commercial complex, represented another prominent American institution. Selecting recognizable buildings made the attacks immediately visible across the world, while their human toll extended far beyond any symbolic purpose the perpetrators assigned to the targets.

United Airlines Flight 93 was the fourth hijacked aircraft. Passengers and crew learned that other aircraft had been used as weapons and resisted their hijackers. The struggle prevented Flight 93 from reaching its intended destination. It crashed in a field near Shanksville, Pennsylvania, killing everyone aboard. The passengers’ action distinguished the final flight from the three that reached buildings, and their resistance became a central part of the history of September 11. The crash site was one of three principal places of loss and remembrance, alongside the World Trade Center and the Pentagon.

The hijackings unfolded within a few hours, but their effects continued throughout the day. Emergency workers searched damaged buildings and debris, hospitals prepared for casualties, and authorities grounded civilian air traffic across the United States. Images of the burning towers, the Pentagon and the collapse in New York established the scale of the disaster before a complete count of victims was possible. The attacks disrupted government, transport and financial activity and led to an immediate search for surviving members of al-Qaeda’s network.

Victims

Al-Qaeda killed 2,977 people in the September 11 attacks. That figure counts victims and excludes the nineteen hijackers, who also died. Those killed included aircraft passengers and crews, people working in the World Trade Center and Pentagon, firefighters, police officers and other emergency personnel. The four aircraft carried people travelling for many reasons; the buildings held employees, visitors and responders. Victims came from the United States and numerous other countries. The final toll therefore represents thousands of distinct families and communities affected by one coordinated operation.

At the World Trade Center, the impacts and subsequent collapses left little time for many occupants to escape, particularly those above the aircraft impact zones. Responders entered while the towers were burning, and many died when the buildings fell. At the Pentagon, the aircraft’s impact killed people both aboard and at work inside. Every passenger and crew member on Flight 93 died after resisting the hijackers. Survivors, witnesses and victims’ families also endured lasting injuries and loss, although the number of wounded varies with the definition used and the period counted.

The victim count is separate from questions about the perpetrators’ citizenship or possible outside assistance. Fifteen hijackers being Saudi nationals does not make Saudi civilians responsible for their crimes. Nor does the presence of Muslims among those killed change the operation’s authorship. Al-Qaeda targeted people without regard to their individual beliefs or roles in American policy. Commemoration of the attacks centers on those killed and on the efforts of passengers, crews and responders who confronted the immediate danger.

Perpetrators and responsibility

Al-Qaeda perpetrated the September 11 attacks with nineteen hijackers under bin Laden’s leadership. Al-Zawahiri helped shape the organization’s direction, and bin al-Shibh served as a logistics coordinator for the plot. Khalid Sheikh Mohammed developed the aircraft operation. Al-Qaeda’s earlier embassy bombings and attack on the USS Cole formed part of its record before 2001; the destruction in New York and at the Pentagon was its most consequential attack against the United States. In an April 2002 video beside bin Laden, al-Zawahiri praised those who carried out the hijackings.

Investigations also examined whether people outside al-Qaeda assisted individual hijackers. Twenty-eight previously classified pages from a congressional Joint Inquiry were released with redactions in July 2016. They described contacts between some hijackers and people who may have been connected to the Saudi government, as well as support or assistance those people may have provided. Some investigators alleged that two possible helpers were Saudi intelligence officers. The Joint Inquiry did not independently verify the accuracy or significance of this material. Its account did not establish whether any Saudi officials knowingly supported the plot or the extent of any government-linked assistance. Civil litigation over possible Saudi responsibility continued years after the attacks.

A separate 2001 review of state sponsorship found no evidence that the Iranian regime sponsored the September 11 operation or knew of it in advance. The finding concerned these attacks specifically and did not settle broader questions about the regime’s support for other armed groups. Investigators’ distinctions between documented al-Qaeda responsibility, possible individual assistance and unproven state direction remain essential to an accurate account of the plot.

False accusations against Israel spread soon after the attacks. Prince Salman bin Abdulaziz, then governor of Riyadh, accused Israel and Mossad of orchestrating them when he met the newly arrived American ambassador. His accusation was false. Stories claiming that Mossad agents celebrated or secretly arranged the attacks likewise became recurring antisemitic conspiracy theories. Mossad had warned American agencies of a major threat before September 11. Al-Qaeda’s planning, nineteen hijackers and subsequent celebration of the operation identify its perpetrators; claims blaming Jews or Israel deflect responsibility from them.

Response

President George W. Bush launched a military campaign in Afghanistan against al-Qaeda and its Taliban protectors. Within weeks of September 11, American forces attacked Taliban and al-Qaeda positions. Operation Enduring Freedom drove the Taliban government from power and forced many of its members into Pakistan. Thousands of al-Qaeda operatives were killed or captured during the initial response, and the organization lost much of the sanctuary and communications structure it had used in Afghanistan. Its remaining members and leaders went into hiding, while cells elsewhere gained greater autonomy as the central network was disrupted.

The response extended beyond Afghanistan. Most Middle Eastern governments froze al-Qaeda assets under United Nations Security Council Resolution 1373. Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates condemned the attacks and took steps against terrorist financing. Some governments gave the American campaign personnel, basing or overflight support. Syria and Lebanon cooperated with investigations into al-Qaeda while refusing to recognize Hezbollah and Hamas as terrorist organizations. Saddam Hussein’s Iraq was the only Arab or Muslim country that did not condemn the attacks.

Inside the United States, preventing further terrorist attacks became the FBI’s leading priority. The bureau centralized counterterrorism investigations, giving headquarters greater authority over cases worldwide. It also developed analytic and intelligence-sharing capacity: a college of analytic studies was created in 2003, an intelligence directorate in 2004, and a National Security Service encompassing counterterrorism and counterintelligence in 2005. These changes reflected the need to connect information gathered in different places before a network could act.

Military operations weakened al-Qaeda without ending the threat from its affiliates and successors. The organization used the internet more extensively for communication, recruitment and propaganda after September 11. The United States remained involved in Afghanistan for two decades before withdrawing in 2021. Its departure closed the military intervention prompted by the attacks, while leaving the wider questions of counterterrorism, civilian protection and the consequences of prolonged war in public debate. The attacks also shaped how governments assessed cross-border networks and cooperation against terrorist financing.

Remembrance

September 11 is commemorated through ceremonies, memorials and the testimony of survivors and families. Remembrance focuses on the 2,977 victims, the resistance aboard Flight 93 and the work of emergency personnel. The anniversary has also been contested in online spaces, where supporters of al-Qaeda and the Islamic State have celebrated the hijackers and mocked those they killed. Their use of the date seeks to turn an act of mass murder into a recruiting symbol.

Al-Qaeda’s own media activity shows that effort across several years. Around the sixth anniversary in 2007, bin Laden released a video and an audio recording that began a nine-month campaign. The September 11 audio presented one World Trade Center hijacker as a model for violent jihad. On the seventeenth anniversary in 2018, al-Qaeda’s media arm released a thirty-minute recording in which al-Zawahiri urged armed jihad against the United States and its allies. On the eighteenth anniversary, he defended the hijackings against religious critics. These messages were attempts to preserve the operation’s status within al-Qaeda’s movement despite the damage the organization had sustained.

Supporters later adapted anniversary propaganda to social media. An al-Qaeda support network on Facebook held a September 11 meme contest in 2020 and 2021. Accounts and channels associated with al-Qaeda and the Islamic State circulated material celebrating the attacks on mainstream and encrypted platforms. During the 2023 Israel–Hamas war, bin Laden’s 2002 “Letter to America” resurfaced online. The letter was not a newly discovered policy critique: it justified al-Qaeda’s murder of people on September 11. On the attacks’ twenty-fifth anniversary in 2026, al-Qaeda supporters circulated another video celebrating them.

Other armed networks also invoked the anniversary. On September 11, 2021, coalition defenses intercepted two explosive drones at Erbil International Airport in Erbil, Iraq. Neither civilians nor coalition personnel were injured. A militia media channel briefly linked the attack to the twentieth anniversary before deleting its message. The episode illustrated how the date could be used beyond al-Qaeda’s own communications, even when the later attack had different perpetrators and circumstances.

September 11 has also remained a subject of false narratives, particularly claims that Jews or Israel organized the hijackings. Such claims erase al-Qaeda’s documented responsibility and replace evidence with antisemitic accusation. Accurate remembrance preserves both the scale of the victims’ loss and the identity of those who inflicted it. The attacks were carried out by nineteen al-Qaeda operatives on four aircraft; they killed 2,977 people and changed American and international security policy for decades.