The Background to September 11, 2001

To understand September 11, 2001, it is necessary to look beyond the morning itself. The attacks were the result of a longer development involving al-Qaeda, Osama bin Laden, political conflicts in the Middle East and Afghanistan, and failures within different parts of the U.S. counterterrorism system.

The 9/11 Commission’s historical account traces the development of al-Qaeda and its leadership during the 1980s and 1990s. The organization gradually developed a strategy aimed at attacking the United States and its interests. Earlier terrorist attacks, including the 1993 World Trade Center bombing and attacks on U.S. targets overseas, demonstrated that transnational terrorism was becoming a serious security concern.

Historical books such as Lawrence Wright’s The Looming Tower and Steve Coll’s Ghost Wars examine the political and organizational history that preceded the attacks. These works are useful because they place September 11, 2001 within a much longer story rather than treating the day as an isolated event.

What Happened on September 11, 2001?

On the morning of September 11, 2001, 19 hijackers took control of four commercial passenger aircraft after their departures from airports on the U.S. East Coast.

Two aircraft were flown into the Twin Towers of the World Trade Center in Lower Manhattan. A third aircraft was flown into the Pentagon in Arlington, Virginia. The fourth aircraft, United Airlines Flight 93, crashed near Shanksville, Pennsylvania after passengers and crew attempted to stop the hijackers.

The attacks were coordinated and unfolded within a little more than three hours. The scale and speed of the events overwhelmed ordinary emergency procedures and forced national leaders, air-traffic controllers, police officers, firefighters, military personnel and civilians to respond under extraordinary conditions.

The 9/11 Memorial & Museum records 2,977 victims of the attacks. The victims came from 90 nations, demonstrating from the beginning that the tragedy was international rather than purely domestic.

September 11, 2001 Timeline

The timeline shows how rapidly the crisis developed. For people watching from New York, Washington and elsewhere, information changed from minute to minute. Television networks broadcast images around the world, making September 11, 2001 one of the first truly global media events of the twenty-first century.

The World Trade Center on September 11, 2001

The World Trade Center was one of the most recognizable symbols of New York City and international commerce. The Twin Towers dominated the Lower Manhattan skyline and housed thousands of workers.

When Flight 11 hit the North Tower and Flight 175 hit the South Tower, fires spread through damaged areas of the buildings. Thousands of people began evacuating while firefighters, police officers and emergency workers moved toward the buildings.

The collapse of the towers created an enormous rescue and recovery operation. The National Institute of Standards and Technology later conducted an extensive investigation into the building performance, evacuation and emergency response.

The Pentagon Attack

At 9:37 a.m., American Airlines Flight 77 struck the Pentagon, the headquarters of the U.S. Department of Defense in Arlington, Virginia.

The Pentagon attack demonstrated that the assault was aimed not only at financial and commercial symbolism. The Pentagon represented U.S. military power and national defense.

Emergency personnel responded to the fire and structural damage while the wider Washington area was placed under an extraordinary security response. The attack also intensified the realization that the country faced a coordinated national emergency.

Flight 93: The Passengers Who Fought Back

United Airlines Flight 93 was traveling toward the West Coast when the hijacking occurred. Passengers and crew members learned through telephone calls that other aircraft had been used in attacks.

They eventually organized an attempt to retake the cockpit. The aircraft crashed into a field near Shanksville, Pennsylvania at 10:03 a.m.

The exact intended target has been the subject of historical analysis, but the 9/11 Commission concluded that the aircraft was heading toward Washington. The actions of the passengers and crew prevented the aircraft from reaching its intended destination.

The Human Cost of September 11, 2001

The most important part of the history is the human cost. The attacks killed 2,977 people. Victims included office workers, airline passengers and crew, firefighters, police officers, emergency medical personnel and people working in or near the affected sites.

The loss continued beyond the day itself. Survivors, rescue workers, recovery workers, families and communities experienced long-term physical, emotional and financial consequences.

The 9/11 Memorial & Museum preserves the names and stories of those killed. Its records emphasize that the victims represented dozens of nations and many different backgrounds.

Remembering the victims is important because historical accounts can sometimes become focused on military operations, political decisions and statistics. Those events matter, but the central historical fact remains that thousands of individual lives were permanently changed or lost.

The Immediate Response

The response to September 11, 2001 involved local emergency services, federal agencies, the military, hospitals, volunteers and ordinary citizens.

In New York City, firefighters and police officers entered the World Trade Center complex while civilians attempted to evacuate. At the Pentagon, emergency workers fought fires and searched damaged areas. Near Shanksville, Pennsylvania, investigators and rescue personnel responded to the Flight 93 crash site.

The federal government also faced an unprecedented continuity-of-government challenge. Air traffic across the United States was halted, aircraft already in the sky were redirected, and national security agencies worked to understand the scale of the attack.

The response demonstrated both remarkable courage and serious institutional weaknesses. Those strengths and weaknesses became important subjects of later investigations.

Investigations and the 9/11 Commission

After the attacks, several investigations examined different aspects of what had happened. One of the most important was the National Commission on Terrorist Attacks Upon the United States, commonly known as the 9/11 Commission.

The commission was created by Congress and tasked with producing a full account of the circumstances surrounding the attacks and recommendations for preventing future terrorist attacks. Its final report examined the history of al-Qaeda, intelligence warnings, aviation security, emergency response and national security policy.

The National Archives now preserves the commission’s records. The archive provides researchers with access to hearings, memorandums, reports and other historical materials.

The September 11 Aftermath

The September 11 aftermath was immediate and enormous. The United States entered a new period in which terrorism became a central issue of national security policy.

Congress passed the Authorization for Use of Military Force in September 2001. The law authorized the president to use necessary and appropriate force against those nations, organizations or persons determined to have planned, authorized, committed or aided the attacks, or those who harbored them.

The United States soon launched military operations in Afghanistan against al-Qaeda and the Taliban government that had provided sanctuary to the organization. The Afghanistan War became one of the longest military conflicts in U.S. history.

The attacks also influenced later debates about the Iraq War, even though Iraq was not responsible for carrying out the September 11 attacks. The 9/11 Commission itself treated the question of Iraq separately from the operational responsibility for 9/11.

The War on Terror and Afghanistan

The phrase “War on Terror” became a defining expression of the post-September 11 period. Counterterrorism moved to the center of American foreign policy, military planning and intelligence work.

Afghanistan became the first major battlefield of the post-9/11 wars. The Taliban regime was removed from power after U.S.-led military operations began in October 2001, although the conflict continued for many years.

The historical consequences were complicated. The intervention destroyed al-Qaeda’s safe haven in Afghanistan but did not immediately end militant activity. The conflict later developed into a prolonged insurgency involving the Taliban, Afghan government forces and international troops.

The post-9/11 military campaigns also raised major questions about civilian casualties, detention, interrogation, intelligence, surveillance, sovereignty and the limits of military power.

How Security Changed After September 11, 2001

Air travel changed dramatically after the attacks. The Aviation and Transportation Security Act became law in November 2001 and established the Transportation Security Administration, or TSA.

Airport screening became more centralized and extensive. Passenger identification, baggage screening, cockpit security and other aviation procedures changed substantially.

The changes extended beyond airports. Intelligence agencies, law enforcement organizations and financial institutions developed new approaches to identifying and disrupting terrorist networks.

The Global Impact of September 11, 2001

The global impact of September 11, 2001 extended far beyond the United States. Governments around the world strengthened counterterrorism laws, intelligence cooperation and airport security.

International institutions also responded. The United Nations Security Council adopted resolutions addressing terrorism, financing and international cooperation.

The attacks affected migration policy, border controls, intelligence sharing and public debates about civil liberties. Muslim communities in many countries also faced increased scrutiny and, in some places, discrimination and hate crimes.

The attacks changed how many governments understood non-state armed groups. Terrorism was no longer treated only as a criminal problem. It increasingly became a central national-security and foreign-policy issue.

The effects were also cultural. Films, books, television programmes, journalism, memorials and museums created a large body of work attempting to explain and remember the attacks.

The Historical Legacy of September 11, 2001

The legacy of September 11, 2001 is still visible in the twenty-first century. Airport security procedures, counterterrorism laws, intelligence structures and military policies were all shaped by the events that began that morning.

The attacks also changed the way governments think about warning signs. The 9/11 Commission emphasized the importance of imagination, information sharing, accountability and institutional reform.

NIST’s technical investigation produced another kind of legacy. Its findings influenced building safety and emergency response practices, showing how historical disasters can lead to changes that protect future generations.

Perhaps the most enduring lesson is that history is rarely the story of one moment. September 11, 2001 was one day, but understanding it requires examining the years before it and the decades that followed.

Books for Further Historical Reading

Readers who want to study September 11, 2001 in greater depth can compare official investigations with carefully researched historical narratives.

• The Looming Tower — Lawrence Wright:
  A detailed history of the rise of al-Qaeda, the development of Islamist militancy and the intelligence failures that preceded the attacks.
  Publisher information
• Ghost Wars — Steve Coll:
  A broader history of Afghanistan, U.S. covert operations, the rise of bin Laden and the background to the emergence of al-Qaeda.
  Publisher information
• The Only Plane in the Sky — Garrett M. Graff:
  An oral history built from interviews, archival material and firsthand accounts of people who experienced the day.
  Publisher information

These books approach the subject differently. The official 9/11 Commission Report is especially useful for institutional history, while narrative histories and oral histories help explain the human experience and the longer political background.

Frequently Asked Questions About September 11, 2001

Official Sources and References