September 11 attacks
The September 11 attacks were a series of four coordinated Islamist terrorist suicide attacks executed by 19 militants affiliated with the extremist group al-Qaeda against targets in the United States on the morning of September 11, 2001.[1][2] The hijackers, mostly Saudi nationals trained in al-Qaeda camps in Afghanistan, seized control of four commercial airliners shortly after takeoff from airports on the East Coast: American Airlines Flight 11 and United Airlines Flight 175 struck the North and South Towers of the World Trade Center in New York City; American Airlines Flight 77 impacted the Pentagon in Arlington, Virginia; and United Airlines Flight 93 crashed into a field near Shanksville, Pennsylvania, following a passenger uprising against the hijackers.[3][4] The operation, masterminded by Khalid Sheikh Mohammed and approved by al-Qaeda leader Osama bin Laden, exploited lapses in domestic aviation security and intelligence sharing to maximize destruction.[5][6] The strikes caused the immediate deaths of 2,977 victims, including office workers, first responders, passengers, and military personnel, with thousands more injured amid fires, structural failures, and debris; this toll excludes the 19 perpetrators and remains the deadliest incident of terrorism in history.[4][7] Both World Trade Center towers collapsed within two hours of impact due to fire-induced structural weakening, as determined by engineering analyses, while the Pentagon sustained significant damage and Flight 93's crash site yielded fragmented wreckage consistent with high-speed impact.[2] Al-Qaeda publicly claimed responsibility, with bin Laden issuing a video admission in 2004 citing U.S. foreign policy in the Middle East as motivation, though empirical evidence from captured operatives and financial trails solidified attribution despite initial intelligence gaps.[8][6] Immediate consequences included unprecedented disruption to air travel, financial markets, and urban infrastructure, with New York City's skyline scarred by the loss of the iconic towers and long-term health effects from toxic dust exposure affecting survivors and responders.[9] The attacks precipitated the U.S.-led Global War on Terror, authorizing the invasion of Afghanistan to dismantle al-Qaeda and oust the Taliban regime that harbored them, while domestic reforms like the PATRIOT Act expanded surveillance powers; notably, the 9/11 Commission found no operational collaboration between al-Qaeda and Iraq's Saddam Hussein, undermining later rationales for the 2003 Iraq invasion.[10][11] Controversies persist over foreknowledge, Saudi governmental involvement—given 15 hijackers' nationalities—and the physics of the tower collapses, which some engineering critiques argue deviated from fire-alone precedents, though official investigations attribute failures to unique impact damages combined with unchecked fires.[6] These events reshaped U.S. security doctrine, prioritizing preemption against non-state actors amid debates on civil liberties erosions and geopolitical overreach.[12]Islamist Origins of the Threat
Al-Qaeda's Ideology and Global Jihad
Al-Qaeda's ideology is rooted in Salafi-jihadism, a radical interpretation of Sunni Islam that combines puritanical Salafism with calls for perpetual armed struggle (jihad) to establish a global caliphate governed by sharia law.[13] This worldview posits a cosmic conflict between true Muslims and a corrupt ummah tainted by Western influence, with jihadists obligated to wage offensive war against apostate regimes and non-Muslim powers perceived as aggressors against Islam.[14] Al-Qaeda leaders, drawing from thinkers like Sayyid Qutb, framed the United States as the primary enemy—"the head of the snake"—whose defeat would cascade to topple local tyrants and restore Islamic dominance, evidenced in operational manuals and recruitment materials emphasizing strategic strikes on the far enemy over near ones.[15][16] Central to this ideology were Osama bin Laden's fatwas, issued as religious edicts binding on followers. In his August 23, 1996, "Declaration of War Against the Americans Occupying the Land of the Two Holy Places," bin Laden condemned the U.S. military presence in Saudi Arabia—numbering around 5,000-10,000 troops post-1991 Gulf War—as a defilement of Islam's holiest sites, Mecca and Medina, invoking historical precedents like the Prophet Muhammad's expulsion of polytheists to mandate jihad as a defensive and purifying duty.[17][18] He cited U.S. bases established after Iraq's invasion of Kuwait as an ongoing occupation enabling Saudi royal corruption, urging Muslims worldwide to kill American forces there regardless of consequences.[19] The ideology escalated in bin Laden's February 23, 1998, fatwa, co-signed by allies including Ayman al-Zawahiri, expanding jihad to target all Americans and their allies, civilian and military, "in any country" where feasible.[18] Grievances included U.S. support for Israel's occupation of Palestinian territories—framed as theft of Muslim land—and sanctions on Iraq post-Gulf War, which bin Laden claimed caused over 500,000 child deaths by 1998, portraying these as deliberate crusader aggression against the ummah.[18] This ruling rejected distinctions between combatants and non-combatants, interpreting Quranic verses on fighting "those who fight you" as license for indiscriminate retaliation, a departure from classical Islamic just war constraints.[18] Unlike mainstream Islamic scholarship, which limits jihad to defensive contexts and prohibits targeting innocents, al-Qaeda's doctrine radicalized a fringe minority by glorifying martyrdom operations and mass casualty attacks as apex religious acts, disseminated via videos and manifestos that appealed to alienated youth with superficial religious knowledge.[20] This selective radicalism, prioritizing takfir (declaring Muslims apostates for insufficient zeal) and global confrontation over reform, enabled recruitment of operatives willing to execute suicide missions, as seen in training camps emphasizing ideological purity over tactical restraint.[13] While claiming to defend Muslims, the ideology's causal engine was supremacist irredentism, viewing Western modernity itself as an existential threat warranting total war.[14]Prior al-Qaeda Operations
Al-Qaeda's operations prior to September 11, 2001, marked an escalation from support for regional insurgencies to direct, high-impact strikes against U.S. interests, employing truck bombs, coordinated embassy assaults, and suicide boat attacks to target symbols of American economic, diplomatic, and military power. These actions, often planned from bases in Sudan and Afghanistan under Osama bin Laden's oversight, demonstrated growing operational sophistication and a focus on inflicting mass casualties on U.S. personnel and allies. Funding for these efforts traced back to bin Laden's financial networks, including donations from wealthy sympathizers and businesses in the Gulf region.[21] The earliest major U.S.-targeted operation linked to al-Qaeda networks occurred on February 26, 1993, when Ramzi Yousef and accomplices detonated a 1,200-pound urea nitrate truck bomb in the parking garage beneath the World Trade Center's North Tower in New York City. The explosion killed six people and injured 1,042 others, causing structural damage that required extensive repairs but failed to topple the towers as intended. Perpetrators, including Yousef (nephew of later al-Qaeda figure Khalid Sheikh Mohammed), were connected to Islamist cells influenced by Sheikh Omar Abdel-Rahman and supported indirectly by bin Laden's emerging organization through training and resources.[22][23][21] By 1998, al-Qaeda had advanced to synchronized transnational attacks, bombing U.S. embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania, on August 7 with truck bombs containing hundreds of pounds of TNT and aluminum powder. These blasts killed 224 people (including 12 Americans) and wounded over 4,500, primarily local staff and passersby, while destroying the embassy buildings and nearby structures. The operations, directed by bin Laden and executed by al-Qaeda cells with logistical aid from East African radicals, underscored the group's ability to project power across continents against U.S. foreign policy outposts.[24][25][21] The pattern continued with a maritime suicide attack on October 12, 2000, when al-Qaeda operatives piloted an explosive-laden skiff alongside the USS Cole during refueling in Aden Harbor, Yemen, detonating approximately 500 pounds of C-4 plastic explosive and shattering the destroyer's hull. The assault killed 17 U.S. sailors and injured 39 others, crippling the $1 billion vessel and exposing security gaps in port visits. Al-Qaeda publicly claimed responsibility, with planning attributed to bin Laden's core operatives, reflecting refined tactics blending small-boat delivery with high-explosive payloads against naval assets.[26][27][21] These incidents revealed al-Qaeda's persistent targeting of U.S. vulnerabilities despite prior captures and indictments of key figures, with each attack building on lessons from the last to amplify lethality and media impact.[21]Key Figures: Osama bin Laden and Khalid Sheikh Mohammed
Osama bin Laden transitioned from a wealthy Saudi family member to a mujahideen fighter in Afghanistan during the Soviet occupation, arriving in Peshawar in the mid-1980s to recruit and fund Arab volunteers against the invaders.[28] He established al-Qaeda in 1988 as a network to sustain jihadist operations post-Soviet withdrawal, emphasizing attacks on perceived enemies of Islam including the United States for its military presence in Saudi Arabia and alliances with Israel.[21] Bin Laden's ideological commitment to global jihad framed the 9/11 attacks as a spectacular operation to provoke American overreaction, drain resources, and rally Muslims, leading him to grant final approval to the plot in mid-1999 after initial reservations about its scale.[29] Khalid Sheikh Mohammed, a Pakistani engineer radicalized through jihadist networks, proposed the "planes operation"—crashing hijacked airliners into U.S. landmarks—to bin Laden in 1996, evolving concepts from the 1994-1995 Bojinka plot he co-planned with nephew Ramzi Yousef, which tested hijackings and bombings but included early ideas of flying planes into CIA headquarters and other targets.[29] As al-Qaeda's chief operational planner, Mohammed refined the 9/11 scheme by selecting targets like the World Trade Center for symbolic economic impact, coordinating logistics, and insisting on suicide missions to maximize casualties, viewing the attacks as retaliation for U.S. foreign policy.[29] Captured on March 1, 2003, in Rawalpindi, Pakistan, he confessed under interrogation to masterminding 9/11 alongside other plots, detailing his direct oversight of hijacker preparations.[30] Other key enablers included Mohammed Atef, al-Qaeda's military commander and bin Laden deputy, who helped integrate the plot into the group's structure and provided training support until his death in a U.S. airstrike on November 16, 2001. Ramzi Yousef, imprisoned since 1997 for the 1993 World Trade Center bombing, indirectly influenced via shared Bojinka tactics with Mohammed, though fragmented U.S. intelligence silos pre-9/11 allowed these figures to evade capture despite prior warnings about their networks.[31]
Planning and Intelligence Context
Development of the Plot
Khalid Sheikh Mohammed first proposed the operational concept of hijacking multiple U.S. commercial airliners and using them as suicide weapons against symbolic targets to Osama bin Laden in mid-1996, but bin Laden deferred the idea at the time due to resource constraints from other al-Qaeda priorities.[32] By spring 1999, following the arrest of Mohammed's nephew in a related plot, Mohammed renewed the pitch during meetings in Afghanistan, emphasizing the psychological impact of crashing planes into high-value sites without need for explosives.[33] Bin Laden approved the scaled-down version targeting East Coast landmarks, designating Mohammed as operational director and allocating up to $500,000 from al-Qaeda's treasury for logistics, travel, and preparations.[32] [34] The selected targets reflected al-Qaeda's strategic focus on economic, military, and political power centers: the World Trade Center towers in New York to symbolize American capitalism, the Pentagon as the seat of U.S. military might, and the U.S. Capitol (or alternatively the White House) for legislative/executive authority.[32] This blueprint evolved through iterative discussions between bin Laden, Mohammed, and al-Qaeda military chief Mohammed Atef, prioritizing aircraft with sufficient fuel loads for maximum destruction upon impact.[32] Over late 1999 and early 2000, bin Laden and Mohammed vetted and selected 19 operatives, 15 of whom were Saudi nationals vetted for ideological commitment, physical fitness, and unremarkable travel histories to evade scrutiny; the remainder included Egyptian, Emirati, and Lebanese members integrated via al-Qaeda training camps.[32] Operational security emphasized compartmentalization: hijacker teams operated semi-independently, using couriers for instructions, coded verbal signals (e.g., references to "weddings" for attacks), and avoidance of traceable emails or calls, with key directives relayed personally in Kandahar.[32] Financing drew from bin Laden's personal fortune, private donors sympathetic to jihad, and Islamic charities funneled through front entities, totaling around $400,000–$500,000; transfers relied on hawala informal value networks for untraceable remittances, supplemented by cash couriered from the UAE and wire instructions disguised as routine business.[34] [35] No direct evidence links state actors to the plot's core funding or approval, though individual facilitators with ties to Gulf donors provided indirect support without governmental orchestration.[34]Hijacker Recruitment, Training, and Entry into the US
The core operational hijackers, including pilots Mohamed Atta, Marwan al-Shehhi, and Ziad Jarrah, emerged from the Hamburg cell in Germany, where they radicalized amid Islamist influences at the al-Quds mosque by 1999. Atta, born in Egypt in 1968, traveled to Afghanistan in late 1999, training at al-Qaeda camps near Kandahar under directives from Mohammed Atef, and along with Shehhi and Jarrah pledged personal loyalty (bay'ah) to Osama bin Laden, positioning them for the plot due to their adaptation to Western environments.[29] Ramzi bin al-Shibh, also from the cell, facilitated coordination but remained abroad as he could not obtain a U.S. visa.[29] Supporting "muscle" hijackers, predominantly Saudi nationals such as Nawaf al-Hazmi and Khalid al-Mihdhar, were selected in spring 1999 through al-Qaeda networks and underwent paramilitary training at camps like Mes Aynak, focusing on close-quarters combat, explosives, and ideological commitment to martyrdom via suicide operations.[29] Khalid Sheikh Mohammed oversaw their integration, providing specialized instruction in Karachi on blending into Western settings and operational security.[29] This training emphasized hijacking feasibility, drawing from prior al-Qaeda experiences, while reinforcing jihadist intent against U.S. targets. Entry into the United States occurred via temporary visas exploited through incomplete vetting, with 15 of the 19 hijackers obtaining B-1/B-2 tourist/business visas, often in Saudi consulates like Jeddah. Atta secured his B-1/B-2 visa on May 18, 2000, in Berlin and entered at Newark on June 3, 2000, overstaying to pursue flight training without initial student authorization.[36] Shehhi entered similarly on May 29, 2000, at Newark after visa issuance on January 18, 2000, in the UAE, later adjusting to M-1 vocational student status on August 9, 2001.[36] Hani Hanjour, pilot for American Airlines Flight 77, received an F-1 student visa on September 25, 2000, in Jeddah but violated terms by skipping required classes after entering December 8, 2000, at Cincinnati.[36] Al-Hazmi and al-Mihdhar, early arrivals, entered Los Angeles on January 15, 2000, on B-1/B-2 visas issued April 1999 in Jeddah, overstaying amid lax entry-exit tracking.[36] Several Saudis used the expedited Visa Express program starting June 2001 for late entries.[36] Flight training commenced post-entry, with Atta and Shehhi starting at Huffman Aviation in Venice, Florida, in July 2000, progressing rapidly to commercial pilot certifications by December 19, 2000, despite Atta's simulator struggles and Shehhi's mid-air errors noted by instructors.[37] Jarrah trained concurrently at the Florida Flight Training Center in Venice, completing multi-engine certification on August 2, 2001.[37] Hanjour, with prior U.S. training in 1996 at Sierra Academy and 1998–1999 at CRM Flight Cockpit Resource Management, refreshed skills in 2001 at Arizona and New Jersey schools, including advanced simulator work.[36] The group resided unassumingly in shared Florida apartments and San Diego housing, funding activities through wire transfers while blending as students.[37] Operational discipline under Atta's leadership involved target casing, such as dry runs on cross-country flights in early 2001, and adherence to al-Qaeda guidance favoring concealable blades over firearms for hijackings. Recovered materials, including Atta's instructions and plot-related documents, directed use of box cutters and knives under four inches—permitted pre-9/11 security rules—to enable surprise assaults without triggering metal detectors, underscoring tactical prioritization of stealth over firepower.[32] This approach, rooted in camp training, sustained low profiles until the attacks.[29]Pre-Attack Warnings and Systemic Failures
On August 6, 2001, the Central Intelligence Agency delivered a President's Daily Brief to President George W. Bush titled "Bin Ladin Determined To Strike in US," which reported that Usama Bin Ladin since 1997 had sought to conduct terrorist attacks inside the United States, citing patterns of suspicious activity in New York such as surveillance of federal buildings and aircraft, as well as historical threats of hijackings.[38] The brief, based on over 40 pieces of intelligence from multiple sources including foreign governments, emphasized Bin Ladin's intent but provided no specific timing, targets, or operational details, reflecting a compilation of longstanding concerns rather than an imminent alert. Four days earlier, on July 10, 2001, FBI Special Agent Kenneth Williams from the Phoenix field office issued an electronic communication, known as the Phoenix Memo, warning headquarters of an inordinate number of individuals of "uncertain background" enrolled in U.S. flight schools, particularly Middle Eastern men pursuing training in large aircraft without evident interest in commercial piloting careers, and urged canvassing other schools for similar patterns potentially linked to terrorism.[39] Despite its prescient elements, the memo languished without broad dissemination or action, as FBI headquarters deemed it insufficiently prioritized amid workload constraints and lack of coordination with CIA aviation threat reporting.[40] These isolated signals exemplified deeper inter-agency dysfunctions, including entrenched rivalries between the CIA and FBI that impeded data sharing on al Qaeda operatives.[32] A critical barrier was the "wall" established by 1995 Justice Department guidelines, which strictly segregated foreign intelligence collection from domestic criminal investigations to safeguard against improper use of evidence, effectively preventing FBI agents from fully accessing CIA-held information on suspects like the hijackers. The 9/11 Commission later documented how this policy, intended to protect civil liberties, fostered a culture of compartmentalization where CIA leads on al Qaeda travel and activities were not promptly relayed to FBI counterterrorism units, despite statutory requirements under the Foreign Intelligence Surveillance Act. Visa processing lapses compounded these issues; for instance, the Immigration and Naturalization Service's automated systems failed to flag overstays or coordinate with intelligence on high-risk entrants, leaving unresolved leads on thousands of cases including those involving Saudi nationals with jihadist ties. Particular missed opportunities underscored the human and procedural toll of these silos, as seen in the handling of hijackers Khalid al-Mihdhar and Nawaf al-Hazmi. The CIA photographed both attending an al Qaeda operational meeting in Kuala Lumpur, Malaysia, from January 5-8, 2000, and confirmed Mihdhar's U.S. visa issuance on April 23, 2000, yet delayed placing either on a watchlist until Mihdhar in late August 2001 and Hazmi not at all pre-9/11, allowing them to enter the U.S. multiple times and settle in San Diego by September 2000.[41] Even after learning in January 2001 of their links to the USS Cole bombing via shared intelligence, the CIA withheld full details from the FBI until late August 2001, citing concerns over source protection and jurisdictional boundaries, despite Mihdhar and Hazmi's open associations with local flight instructors and attendance at mosques known to radicals.[38] This non-pursuit persisted amid their visa expirations and suspicious activities, such as Hazmi's multiple address changes and interactions with other plot participants. Broader institutional shortcomings included a failure to fully grasp al Qaeda's adaptive tactics, characterized by the 9/11 Commission as deficiencies in imagination, policy, capabilities, and management, where analysts did not envision the weaponization of commercial airliners despite precedents like the thwarted 1995 Bojinka plot to explode U.S.-bound planes.[42] U.S. agencies underestimated the persistent threat from Islamist extremists inspired by Bin Ladin's global jihad declaration, partly due to resource allocation favoring state actors over non-state networks and a post-Cold War pivot that deprioritized counterterrorism. Critiques in the Commission's findings and subsequent reviews pointed to hesitancy in prioritizing ideological profiling of jihadist indicators—such as repeated attendance by Saudi and Yemeni males at radical training—over generalized threat assessments, influenced by domestic sensitivities around targeting specific ethnic or religious groups despite empirical patterns in al Qaeda recruitment and operations. These factors collectively enabled the plot to advance unchecked, as disconnected warnings failed to trigger proactive measures like enhanced airport security or unified field investigations.[32]Execution of the Attacks
Hijacking Sequence and Crash Timeline
American Airlines Flight 11, a Boeing 767 bound from Boston's Logan International Airport to Los Angeles International Airport, departed at 7:59 a.m. Eastern Daylight Time (EDT).[43] The aircraft carried 81 passengers, 11 crew members, and five hijackers, including pilot-trained Mohamed Atta.[32] Hijackers initiated the takeover around 8:14 a.m., using box cutters and mace to stab flight attendants and gain access to the cockpit, as reported in calls from attendant Betty Ong to ground personnel describing stabbings and passenger injuries.[44] Air traffic control (ATC) logs captured the hijackers' announcement over the radio: "We have some planes. Just stay quiet and you'll be okay."[32] The transponder was disabled at 8:21 a.m., and the plane deviated sharply southward; it crashed into the North Tower of the World Trade Center at 8:46 a.m.[45] United Airlines Flight 175, another Boeing 767 on the same Boston-to-Los Angeles route, departed Logan at 8:14 a.m. with 56 passengers, 9 crew, and five hijackers led by Marwan al-Shehhi.[46] The hijacking occurred between 8:42 a.m. (last routine communication) and 8:46 a.m., with hijackers employing similar tactics of knives and threats of a bomb to control the cabin, per ATC observations of erratic maneuvers and a turned-off transponder.[44][32] Flight attendants relayed details of the assault via airphone calls, noting slain crew and restricted cockpit access.[46] The aircraft turned sharply toward New York City and struck the South Tower at 9:03 a.m.[45] American Airlines Flight 77, a Boeing 757 departing Washington Dulles International Airport for Los Angeles at 8:20 a.m., carried 58 passengers, 6 crew, and five hijackers including Hani Hanjour as pilot.[47] Hijackers seized control around 8:51-8:54 a.m., slashing throats of crew members and claiming a bomb, as inferred from flight data recorder (FDR) recovery showing cockpit intrusion and passenger calls reporting violence.[44][32] The transponder code changed multiple times before going dark, and the plane executed a 330-degree descending spiral; it impacted the Pentagon at 9:37 a.m.[48][45] United Airlines Flight 93, a Boeing 757 delayed from Newark Liberty International Airport to San Francisco and airborne at 8:42 a.m., had 37 passengers, 7 crew, and four hijackers with Ziad Jarrah trained as pilot.[49] The hijacking began around 9:28 a.m., with cockpit voice recorder (CVR) data capturing stabbings, mace deployment, and threats of a bomb to subdue passengers.[44][32] Passengers, informed via airphones of earlier attacks, revolted starting at approximately 9:57 a.m., storming the cockpit amid sounds of struggle recorded on the CVR.[49] The plane crashed in a field near Shanksville, Pennsylvania, at 10:03 a.m. after hijackers pitched it nose-down.[45][49]| Flight | Departure Time (EDT) | Hijacking Onset | Crash Time (EDT) | Key Evidence Sources |
|---|---|---|---|---|
| AA11 | 7:59 a.m. | ~8:14 a.m. | 8:46 a.m. | ATC logs, Ong calls[32] |
| UA175 | 8:14 a.m. | 8:42-8:46 a.m. | 9:03 a.m. | ATC, airphone calls[46] |
| AA77 | 8:20 a.m. | ~8:51 a.m. | 9:37 a.m. | FDR, passenger calls[47] |
| UA93 | 8:42 a.m. | ~9:28 a.m. | 10:03 a.m. | CVR, airphone calls[49] |