On September 11, 2001, the United States experienced a series of coordinated terrorist attacks that killed 2,977 people and became one of the defining events of the early 21st century.

What happened, in brief

  • Nineteen hijackers linked to the extremist group al‑Qaeda took control of four commercial airplanes departing from U.S. airports on the East Coast.
  • Two planes were flown into the Twin Towers of the World Trade Center in New York City, leading to the collapse of both towers and severe destruction in Lower Manhattan.
  • A third plane struck the Pentagon, the headquarters of the U.S. Department of Defense, in Arlington, Virginia.
  • The fourth plane, United Flight 93, crashed in a field near Shanksville, Pennsylvania, after passengers resisted the hijackers; it is widely believed the hijackers were aiming for a target in Washington, D.C., such as the White House or the U.S. Capitol.

Basic timeline (morning of 9/11)

  • Around 8:46 a.m.: American Airlines Flight 11 hits the North Tower of the World Trade Center in New York City.
  • 9:03 a.m.: United Airlines Flight 175 hits the South Tower.
  • 9:37 a.m.: American Airlines Flight 77 crashes into the Pentagon.
  • 9:59 a.m.: The South Tower of the World Trade Center collapses.
  • 10:02 a.m.: United Airlines Flight 93 crashes in a field near Shanksville, Pennsylvania, after passengers attempt to retake the plane.
  • 10:28 a.m.: The North Tower collapses.

The four planes (quick view)

[5][1][7] [1][5][7] [5][7][1] [3][1][5]
Flight From → To What happened
American Airlines 11 Boston → Los Angeles Hijacked and flown into the World Trade Center North Tower at 8:46 a.m.
United Airlines 175 Boston → Los Angeles Hijacked and flown into the South Tower at 9:03 a.m.
American Airlines 77 Washington Dulles → Los Angeles Hijacked and crashed into the Pentagon at 9:37 a.m.
United Airlines 93 Newark → San Francisco Hijacked; passengers fought back, and it crashed in a Pennsylvania field at 10:02 a.m., likely preventing an attack in Washington, D.C.

Human impact and immediate aftermath

  • In total, 2,977 victims were killed, not counting the 19 hijackers; most were civilians, including people in the buildings, airplane passengers and crew, and first responders.
  • Thousands more were injured, and many survivors and rescue workers later developed long‑term health problems from dust, smoke, and toxic debris, especially around the World Trade Center site.
  • Fires and wreckage at the World Trade Center site burned and smoldered for months, and surrounding buildings were badly damaged or collapsed, including World Trade Center Building 7 later that day.

How it changed the world

  • The attacks led the U.S. to launch the “War on Terror,” including the invasion of Afghanistan to remove the Taliban regime that had harbored al‑Qaeda leadership.
  • New security and surveillance measures were put in place worldwide, such as stricter airport screening, expanded intelligence programs, and new laws like the U.S. Patriot Act.
  • The site of the Twin Towers in New York, often called Ground Zero, eventually became home to One World Trade Center and the National September 11 Memorial & Museum, which honor the victims and first responders.

Different perspectives and ongoing discussion

  • For many Americans and people around the world, 9/11 is remembered as a day of shock, grief, and extraordinary acts of courage, especially by firefighters, police, medical personnel, and ordinary civilians helping each other.
  • Historians and policy experts continue to debate how the attacks reshaped U.S. foreign policy, civil liberties, and public attitudes toward security, war, and immigration.
  • Each year, memorial ceremonies and moments of silence are held on September 11 to remember those who were killed and the lasting consequences of that day.

“What happened on September 11th, 2001?” is not only about the attacks themselves but also about how they transformed politics, security, and everyday life in the U.S. and far beyond.

TL;DR: On September 11, 2001, al‑Qaeda terrorists hijacked four planes, crashing two into the World Trade Center in New York, one into the Pentagon, and one into a Pennsylvania field after passenger resistance, killing 2,977 people and triggering major global political, military, and security changes.

Information gathered from public forums or data available on the internet and portrayed here.