An outline, era by era

September 11 attacks (2001) and the War on Terror

21st Century · 2000 – present

On the morning of 11 September 2001, nineteen hijackers linked to the al-Qaeda network seized four passenger aircraft in the United States. Two were flown into the towers of the World Trade Center in New York and one into the Pentagon near Washington, D.C. The fourth crashed in a field in Pennsylvania after passengers tried to retake it. Nearly 3,000 people were killed, the deadliest attack on United States soil.

In response the United States and its allies launched what the administration of George W. Bush called the War on Terror. It began with the invasion of Afghanistan in October 2001 to remove the Taliban government that had sheltered al-Qaeda. It grew to include the Iraq War from 2003, new security laws, detention at Guantánamo Bay, drone strikes and expanded surveillance. These conflicts shaped politics, law and international relations for two decades, and Western forces left Afghanistan in 2021.

Things happened, and the rest is history

  1. Al-Qaeda and the Afghan jihad

    Event

    What happened

    After the Soviet invasion of Afghanistan in December 1979, foreign volunteers, including Osama bin Laden, join the resistance, and the Soviet Union withdraws in 1989. In 1988 bin Laden and others found al-Qaeda as a network of veterans. In the 1990s bin Laden moves to Sudan and then, in 1996, back to Afghanistan, where the Taliban later take power.

    The rest is history

    Al-Qaeda issued declarations of war on the United States in 1996 and 1998, citing the US military presence in Saudi Arabia and US policy in the Middle East. Afghanistan gave it a base for training and planning. The 9/11 Commission treated this sanctuary as central to the plot. It also explains why Afghanistan was the first target of the American response in 2001.

    Sources

    1. PrimaryNational Commission on Terrorist Attacks Upon the United States. The 9/11 Commission Report. Washington, D.C.: Government Printing Office, 2004.
    2. BookWright, Lawrence. The Looming Tower: Al-Qaeda and the Road to 9/11. New York: Alfred A. Knopf, 2006.

  2. The 1998 embassy bombings and the USS Cole

    Event

    What happened

    On 7 August 1998 truck bombs explode almost simultaneously at the US embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania, killing more than 200 people, most of them Africans. The United States blames al-Qaeda and fires cruise missiles at targets in Afghanistan and Sudan on 20 August. In October 2000 a suicide boat attack on the destroyer USS Cole in Aden, Yemen, kills 17 American sailors.

    The rest is history

    These attacks showed that al-Qaeda could strike overseas, and American prosecutors indicted bin Laden in 1998. The missile strikes did not stop the network. The 9/11 Commission described them as part of a pattern of attacks that US policy had not halted before 2001. The 9/11 plot was approved around 1999 and carried out two years later.

    Sources

    1. PrimaryNational Commission on Terrorist Attacks Upon the United States. The 9/11 Commission Report. Washington, D.C.: Government Printing Office, 2004.
    2. BookBergen, Peter L. The Osama bin Laden I Know. New York: Free Press, 2006.

  3. The plot takes shape

    Event

    What happened

    Khalid Sheikh Mohammed proposes an aircraft plot to bin Laden in 1996, and it is approved around 1999. Several future hijackers, including Mohamed Atta, form a cell in Hamburg and travel to Afghanistan. Most of the nineteen men were Saudi nationals. In 2000 and 2001 some of them train as pilots at flight schools in the United States.

    The rest is history

    The attackers entered the country on valid visas. Warning signs were scattered across agencies, including a CIA cable about two future hijackers and an FBI memo from Phoenix. The agencies did not combine them in time. The 9/11 Commission called this a failure of imagination, policy, capabilities and management. It led directly to a major reorganisation of American intelligence.

    Sources

    1. PrimaryNational Commission on Terrorist Attacks Upon the United States. The 9/11 Commission Report. Washington, D.C.: Government Printing Office, 2004.

  4. The attacks of 11 September 2001

    Event

    What happened

    On the morning of 11 September 2001 hijackers take control of four aircraft. American Airlines Flight 11 hits the North Tower at 8:46 a.m. and United Airlines Flight 175 hits the South Tower at 9:03. American Airlines Flight 77 hits the Pentagon at 9:37, and the towers collapse later that morning. United Airlines Flight 93 crashes near Shanksville, Pennsylvania, at about 10:03 after passengers fight the hijackers.

    The rest is history

    The attacks killed nearly 3,000 people, apart from the hijackers, and many rescuers later suffered illness linked to the dust. US airspace was closed for days. NATO invoked its mutual defence clause, Article 5, for the first time on 12 September. Within weeks the United States prepared its military response in Afghanistan.

    Sources

    1. PrimaryNational Commission on Terrorist Attacks Upon the United States. The 9/11 Commission Report. Washington, D.C.: Government Printing Office, 2004.
    2. PrimaryNATO. Statement by the North Atlantic Council, 12 September 2001, invoking Article 5 of the North Atlantic Treaty.

  5. The authorization for use of military force and the Patriot Act

    Event

    What happened

    On 14 September 2001 the US Congress passes the Authorization for Use of Military Force, allowing the president to use force against those responsible for the attacks. On 26 October President Bush signs the USA PATRIOT Act, which widens surveillance and information sharing. In November 2002 the Department of Homeland Security is created.

    The rest is history

    The 2001 authorization has been cited by successive administrations to justify operations against al-Qaeda and related groups in many countries. The new laws widened government powers and sparked a long debate over security and civil liberties. In 2013 leaks by Edward Snowden revealed the scale of electronic surveillance. Parts of the Patriot Act were later changed by the USA Freedom Act of 2015.

    Sources

    1. PrimaryAuthorization for Use of Military Force, Public Law 107-40. United States Congress, 18 September 2001.
    2. PrimaryUniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism (USA PATRIOT) Act, Public Law 107-56. United States Congress, 26 October 2001.

  6. The invasion of Afghanistan

    Event

    What happened

    The Taliban refuse to hand over bin Laden, and on 7 October 2001 the United States and Britain begin air strikes in Afghanistan. Working with the Northern Alliance and with American special forces, they take Kabul in November. The Taliban government falls in December. Bin Laden escapes, and fighting at Tora Bora in December fails to capture him.

    The rest is history

    The Bonn Agreement of December 2001 set up an interim government under Hamid Karzai, and a UN-authorised force, ISAF, was formed. The Taliban regrouped in Pakistan and an insurgency grew from the mid-2000s. Foreign troops numbered over 100,000 at their peak around 2010. After a 2020 agreement in Doha the last Western forces left in 2021, and the Taliban retook Kabul on 15 August 2021.

    Sources

    1. PrimaryAgreement on Provisional Arrangements in Afghanistan Pending the Re-Establishment of Permanent Government Institutions (Bonn Agreement). Bonn, 5 December 2001.
    2. BookColl, Steve. Ghost Wars: The Secret History of the CIA, Afghanistan, and Bin Laden. New York: Penguin Press, 2004.

  7. The Iraq War

    Event

    What happened

    In 2002 and early 2003 the United States and Britain argue that Iraq under Saddam Hussein holds weapons of mass destruction and defies UN resolutions. Without a new Security Council resolution authorising force, a US-led coalition invades on 20 March 2003. Baghdad falls in April, and Saddam is captured in December.

    The rest is history

    No stockpiles of weapons of mass destruction were found, as the Iraq Survey Group reported in 2004. The occupation was followed by a long insurgency and sectarian violence, and the war killed very many Iraqis, with estimates varying widely. American combat forces withdrew in 2011. The war also helped create conditions for the rise of the Islamic State group from 2013 to 2014. It remains deeply controversial, and Britain's Chilcot Report in 2016 criticised the planning and the case for war.

    Sources

    1. PrimaryThe Report of the Iraq Inquiry (Chilcot Report). London: House of Commons, 6 July 2016.
    2. BookRicks, Thomas E. Fiasco: The American Military Adventure in Iraq. New York: Penguin Press, 2006.

  8. Guantánamo, detention and the torture debate

    Event

    What happened

    From January 2002 the United States holds prisoners captured in the War on Terror at the naval base at Guantánamo Bay, Cuba, and in secret CIA facilities. Government lawyers write memos in 2002 that allow harsh interrogation methods. In 2004 photographs from Abu Ghraib prison in Iraq show abuse by US personnel.

    The rest is history

    The US Supreme Court ruled in Rasul v. Bush (2004) and Boumediene v. Bush (2008) that detainees could challenge their detention in US courts. A 2014 US Senate committee report found that the CIA's interrogation programme was more brutal than it had told officials and did not yield key intelligence. President Barack Obama banned the use of those methods in 2009. About 780 men were held at Guantánamo in total, and the facility still held a small number of prisoners in 2024.

    Sources

    1. PrimaryBoumediene v. Bush, 553 U.S. 723. Supreme Court of the United States, decided 12 June 2008.
    2. PrimarySenate Select Committee on Intelligence. Committee Study of the Central Intelligence Agency's Detention and Interrogation Program. Washington, D.C.: United States Senate, 2014.

  9. Iraq and the 9/11 link

    Popular belief

    The legend

    It is often said that Saddam Hussein's Iraq was behind the September 11 attacks, or that Iraq and al-Qaeda were working together. Polls in the United States in 2003 showed that many people believed this. The belief was used to support the war in Iraq.

    The rest is history

    The 9/11 Commission found no collaborative operational relationship between Iraq and al-Qaeda. Contacts had taken place in the 1990s, but Iraq did not support the attacks. Bin Laden, an Islamist, was hostile to Saddam's secular government. The administration's main public case for war was weapons of mass destruction, and the 2004 report of the Iraq Survey Group found no stockpiles. Many Americans nonetheless held the belief for years.

    Sources

    1. PrimaryNational Commission on Terrorist Attacks Upon the United States. The 9/11 Commission Report. Washington, D.C.: Government Printing Office, 2004.
    2. PrimaryCentral Intelligence Agency, Iraq Survey Group. Comprehensive Report of the Special Advisor to the DCI on Iraq's WMD. 2004.

  10. Controlled demolition and inside job claims

    Popular belief

    The legend

    Some people claim the World Trade Center towers were brought down by planted explosives, and that the US government planned or allowed the attacks. Supporters of the idea point to the fall of the smaller Building 7 and to the melting of steel. Videos spread widely online from the mid-2000s.

    The rest is history

    The National Institute of Standards and Technology investigated the collapses and concluded that fires started by the aircraft and burning debris weakened the structural steel. For Building 7 it found that fire caused the failure of a key column. It found no evidence of explosives, and steel does not need to melt to lose much of its strength. The 9/11 Commission found the attacks were planned and carried out by al-Qaeda. NIST published its final report on the towers in 2005 and on Building 7 in 2008.

    Sources

    1. PrimaryNational Institute of Standards and Technology. Final Report on the Collapse of the World Trade Center Towers (NCSTAR 1). Gaithersburg, MD: NIST, 2005.
    2. PrimaryNational Institute of Standards and Technology. Final Report on the Collapse of World Trade Center Building 7 (NCSTAR 1A). Gaithersburg, MD: NIST, 2008.

  11. Bin Laden's death

    Popular belief

    The legend

    It is often said that the killing of Osama bin Laden ended al-Qaeda and the War on Terror. Another version says the raid never happened, or that he had died years earlier. Both stories circulated after the news in 2011.

    The rest is history

    On 2 May 2011 US Navy SEALs killed bin Laden in a compound in Abbottabad, Pakistan, and President Obama announced it that night. Evidence from the compound and the account of participants support the raid. Al-Qaeda continued under Ayman al-Zawahiri, who was himself killed in a US strike in Kabul in 2022. Affiliated groups remained active in several regions, and the Islamic State emerged as a rival. The wider conflicts continued for years after the raid.

    Sources

    1. PrimaryObama, Barack. Remarks by the President on Osama bin Laden. Washington, D.C.: The White House, 2 May 2011.
    2. BookBergen, Peter L. Manhunt: The Ten-Year Search for Bin Laden from 9/11 to Abbottabad. New York: Crown, 2012.

  12. The War on Terror ended with the Afghan withdrawal

    Popular belief

    The legend

    It is sometimes said that the War on Terror ended in 2021 when the last American troops left Kabul. Others say it never really began as a single war. The phrase is used loosely in both ways.

    The rest is history

    The phrase was used by President Bush on 20 September 2001, and later administrations used it less. The Obama administration moved away from it, but kept many of the military and legal tools. Troops left Afghanistan by 30 August 2021, after the Taliban retook Kabul. US forces and counterterrorism operations continued in other places, including Iraq, Syria and Somalia. The 2001 authorization for use of military force also remained in law.

    Sources

    1. PrimaryBush, George W. Address to a Joint Session of Congress and the American People. Washington, D.C., 20 September 2001.
    2. BookJackson, Richard. Writing the War on Terrorism: Language, Politics and Counter-Terrorism. Manchester: Manchester University Press, 2005.

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