On the morning of September 11, 2001, 19 members of al-Qaeda hijacked four commercial passenger aircraft as part of a coordinated terrorist attack against the United States.
The first plane, American Airlines Flight 11, struck the North Tower of New York City's World Trade Center at 8:46 a.m. Seventeen minutes later, United Airlines Flight 175 hit the South Tower.
At 9:37 a.m., American Airlines Flight 77 crashed into the Pentagon in Arlington, Virginia.
The fourth aircraft, United Airlines Flight 93, crashed into a field near Shanksville, Pennsylvania, at 10:03 a.m. The 9/11 Commission concluded that its intended target was likely the U.S. Capitol or the White House, and that passengers who learned what had happened aboard the other flights attempted to retake the aircraft.
The South Tower collapsed at 9:59 a.m. The North Tower followed at 10:28 a.m.
A total of 2,977 people were killed in the attacks, excluding the 19 hijackers. The victims included passengers and crew members aboard the four aircraft, people working in and around the World Trade Center and Pentagon, and emergency responders who entered the buildings to help others.
The losses among first responders were particularly severe. The New York City Fire Department lost 343 firefighters, while the Port Authority Police Department lost 37 officers and the New York Police Department lost 23 officers.
Who carried out the attacks?
The attacks were organized by al-Qaeda, the militant Islamist organization led at the time by Osama bin Laden.
The 9/11 Commission found that the operation developed over several years. Khalid Sheikh Mohammed proposed an aviation-based attack to bin Laden, and preparations eventually centered on using hijacked aircraft as weapons.
The 19 hijackers entered the United States and spent months preparing for the operation. Several received flight training, while others were responsible for supporting the operation and taking control of the aircraft.
The attacks did not emerge without warning. Al-Qaeda had already carried out or attempted attacks against American interests, including the 1998 bombings of U.S. embassies in Kenya and Tanzania and the 2000 attack on the USS Cole.
In February 1993, terrorists had also attempted to destroy the World Trade Center using a truck bomb. That attack killed six people and injured more than 1,000.
Why wasn't 9/11 prevented?
One of the central questions examined after the attacks was how such a large operation could have succeeded despite the existence of U.S. intelligence and security agencies.
The 9/11 Commission found failures across multiple institutions rather than identifying a single cause.
Information about al-Qaeda and several future hijackers existed within the U.S. intelligence and law-enforcement systems, but agencies did not effectively connect or act upon all of the available information.
The aviation security system was also designed primarily around the possibility of traditional hijackings, in which terrorists might take control of an aircraft and use passengers as leverage. It was not prepared for hijackers intending to deliberately crash passenger aircraft into buildings.
The response to the attacks also exposed serious communication and coordination problems between the Federal Aviation Administration, the military and other agencies.
The Commission ultimately described September 11 as both a devastating surprise and a failure to recognize and act on warning signs that had accumulated beforehand.
The immediate aftermath
The attacks triggered an enormous emergency response in New York, Virginia and Pennsylvania.
Lower Manhattan became the site of one of the largest rescue and recovery operations in American history. Thousands of firefighters, police officers, paramedics, construction workers, volunteers and other personnel participated in the response.
The destruction of the World Trade Center also created a massive environmental disaster. Dust and debris covered Lower Manhattan, while fires continued burning at Ground Zero for weeks.
The attacks affected far more people than those killed that day. Survivors, first responders and people who lived or worked near the World Trade Center experienced physical and psychological consequences that continued for years.
Many first responders and other people exposed to the disaster later developed illnesses associated with exposure to the dust and toxic substances released by the collapse and fires.
America after September 11
The attacks fundamentally changed U.S. foreign and domestic policy.
On September 14, Congress authorized the president to use military force against those responsible for the attacks. On October 7, 2001, the United States and its allies began military operations in Afghanistan against al-Qaeda and the Taliban government that had provided sanctuary to bin Laden's organization.
The United States subsequently entered a much broader era of counterterrorism operations.
At home, Congress passed the USA PATRIOT Act, expanding government authorities relating to surveillance, intelligence gathering and terrorism investigations.
The federal government also created the Department of Homeland Security, bringing together numerous agencies and responsibilities under a new cabinet-level department.
Air travel changed dramatically. Airport security became more centralized, cockpit doors were strengthened, passenger screening expanded and the Transportation Security Administration was established.
The war that followed
The consequences of 9/11 extended well beyond Afghanistan.
In 2003, the United States invaded Iraq, citing concerns including Iraq's alleged possession of weapons of mass destruction and its potential connection to terrorism.
The 9/11 Commission did not conclude that Iraq had been responsible for the September 11 attacks.
That distinction became particularly important in the years that followed, as the wars in Afghanistan and Iraq became intertwined in public discussion despite having different origins and rationales.
The Iraq War, in particular, became one of the most controversial decisions of the post-9/11 period.
A lasting debate over security and freedom
The legacy of September 11 remains complicated.
Many of the security measures introduced afterward were intended to prevent another attack. Some became widely accepted parts of everyday life. Others generated sustained debate over privacy, government surveillance, civil liberties, immigration and the balance between security and individual rights.
The attacks also affected Muslim and Arab communities in the United States and elsewhere. Hate crimes and discrimination increased after September 11, while governments and communities faced difficult questions about how to combat terrorism without treating entire religious or ethnic populations as responsible for the actions of extremists.
The distinction remains important: al-Qaeda's ideology and actions do not represent Islam or Muslims generally.
Remembering the people, not only the event
September 11 is often remembered through images of the World Trade Center towers, smoke rising over Manhattan and the moment Americans realized their country was under attack.
But the event was ultimately experienced by thousands of individuals.
There were passengers who boarded planes expecting ordinary flights. Workers beginning another morning at the World Trade Center. Pentagon employees arriving for work. Firefighters and police officers responding to an emergency they did not yet understand. Families waiting for loved ones who would never come home.
Twenty-five years later, the historical significance of September 11 is enormous. But behind the geopolitical consequences and political debates are 2,977 people whose lives ended that day.
Understanding September 11 requires remembering both: the enormous consequences of the attacks and the individual human lives at their center.
Sources
- 9/11 Commission, The 9/11 Commission Report
- National Archives, records relating to the September 11 attacks
- Federal records and investigations concerning the attacks and their aftermath
HUGE's reporting on historical events is based on established primary sources and documented historical evidence. Where facts remain disputed or uncertain, they should be identified as such rather than presented as established fact.