Battles & Wars › Modern conflicts › War on Terror
September 11 attacks
September 11, 2001· Event· Americas
Well documentedSolid records, physical evidence or scientific consensus.
Al-Qaeda hijackers seized four US airliners and crashed them into the World Trade Center, the Pentagon and a Pennsylvania field.
See it on the Battles & Wars map →What happened
On the morning of September 11, 2001, 19 hijackers, 15 of them Saudi citizens, took over four planes. Two struck the twin towers in New York, which collapsed within two hours; one hit the Pentagon outside Washington. On the fourth, passengers fought back and it crashed near Shanksville, Pennsylvania. Nearly 3,000 people were killed, the deadliest terrorist attack in history. The plot was directed by Osama bin Laden and planned by Khalid Sheikh Mohammed.
Why it matters
It led directly to the War on Terror and the invasion of Afghanistan, and brought sweeping changes to air travel, security and US surveillance law.
How we know
The 9/11 Commission Report (2004), flight and cockpit recordings, phone calls from passengers, al-Qaeda's own statements and videos, and evidence recovered from the sites.
Still debated
Questions remain about possible support for some hijackers from Saudi officials; the declassified '28 pages' and later FBI files are still argued over.
Connections (5)
▸Soviet–Afghan War spawned the jihadist networks behind September 11 attacksMostly agreed
The connection
Thousands of foreign Muslim volunteers, the 'Afghan Arabs', went to fight the Soviets, among them Osama bin Laden. In 1988 he and others founded al-Qaeda to carry jihad beyond Afghanistan. Victory over one superpower convinced them they could defeat another, and Afghanistan later became their base under the Taliban.
When and how
Peshawar, Pakistan and eastern Afghanistan in the 1980s; al-Qaeda founded in 1988; bin Laden returned to Afghanistan in 1996.
How sure are we?
The 9/11 Commission Report and al-Qaeda's own statements trace the group to the Afghan jihad, which bin Laden often cited.
Debates and open questions
Whether US aid indirectly helped al-Qaeda is disputed: the CIA funneled aid through Pakistan to Afghan fighters, not to Arab volunteers like bin Laden.
▸September 11 attacks launched War on TerrorWell documented
The connection
Nine days after the attacks, President Bush told Congress the war on terror would not end until every terrorist group of global reach was defeated. Congress had already passed an Authorization for Use of Military Force (AUMF), still used two decades later to justify strikes on al-Qaeda and related groups.
When and how
Washington, September 14–20, 2001: Congress passed the AUMF on September 14, and Bush addressed Congress on September 20.
How we know
The text of the AUMF and Bush's speech are public; later administrations' legal opinions cite the AUMF.
Debates and open questions
Whether a 'war' framing was right, rather than treating terrorism mainly as crime, and how far the AUMF stretches, are still debated.
▸September 11 attacks triggered War in Afghanistan (2001–2021)Well documented
The connection
Afghanistan's Taliban government sheltered bin Laden and refused US demands to hand him over. Less than four weeks after 9/11, US and British forces began strikes, after NATO had invoked Article 5, its mutual-defense clause, for the first time. The Taliban fell by December 2001, but bin Laden escaped.
When and how
Afghanistan, from October 7, 2001; NATO invoked Article 5 on September 12, 2001; the battle of Tora Bora was fought in December 2001.
How we know
US demands, Taliban responses, NATO decisions and military records are public and well documented.
Debates and open questions
Whether more negotiation might have gotten the Taliban to hand bin Laden to a third country, and how he escaped Tora Bora, are debated.
▸Battle of Mogadishu ('Black Hawk Down') was cited by bin Laden before September 11 attacksMostly agreed
The connection
Osama bin Laden repeatedly pointed to the US withdrawal from Somalia as proof America would retreat once its soldiers died. In his 1996 declaration of war and later interviews he cited Mogadishu to recruit followers, part of the reasoning behind al-Qaeda's escalating attacks that culminated on September 11, 2001.
When and how
Bin Laden's August 1996 declaration of jihad and his 1997 CNN and 1998 ABC interviews; al-Qaeda was based first in Sudan, then Afghanistan.
How sure are we?
The 9/11 Commission Report (2004) and bin Laden's own published statements record the Somalia argument.
Debates and open questions
Al-Qaeda's claim to have trained or aided Somali fighters in 1993 is disputed; how much Somalia, rather than other grievances, shaped 9/11 is debated.
▸Killing of Osama bin Laden (Operation Neptune Spear) killed the al-Qaeda leader behind September 11 attacksWell documented
The connection
Bin Laden founded al-Qaeda and approved the 9/11 plot, which Khalid Sheikh Mohammed planned. After the attacks the US demanded the Taliban hand him over; he escaped at Tora Bora in December 2001. Finding him became the War on Terror's most personal goal, achieved nearly ten years later.
When and how
From September 2001 to May 2, 2011: a CIA hunt across Afghanistan and Pakistan ending at Abbottabad; President Obama's announcement cited the 9/11 victims.
How we know
Bin Laden claimed responsibility in a 2004 video, the 9/11 Commission documented his role, and files seized at Abbottabad show him still directing al-Qaeda.
Debates and open questions
Whether his death weakened al-Qaeda much, since the group had already decentralized, and whether his 2001 escape at Tora Bora was avoidable, are still argued.