Carlos Williams was running late on September 11, 2001. At 8:46 that morning, he was rushing down the street toward Stuyvesant High School in New York City, where he had started ninth grade just days earlier. Suddenly, a huge airplane flew low overhead and smashed into the upper floors of the North Tower of the World Trade Center, just a few blocks away.

“I felt the heat from that explosion,” says Williams, now 39. “It was a moment of disbelief.”

Uncertain how to make sense of what he’d just seen, Williams hurried into his school as fire trucks and police cars raced toward the burning building. In his English class on the ninth floor, students pressed against the windows, straining to see what was happening outside.

What Williams and his classmates witnessed was the start of the deadliest foreign attack that the United States has ever experienced on its own soil.

On that day, 19 terrorists hijacked four commercial planes and turned them into airborne weapons. They flew two jets full of passengers into New York’s 110-story-tall Twin Towers, causing the iconic skyscrapers to catch fire and collapse with thousands of people trapped inside.

The second plane crashed into the South Tower at 9:03 a.m., 17 minutes after the first plane hit. Thirty-four minutes later, hijackers flew a third plane that had been en route from Virginia to Los Angeles into the Pentagon—the Department of Defense headquarters—outside Washington, D.C. A fourth plane, immortalized as United Flight 93, crashed shortly afterward in rural Pennsylvania, brought down as passengers bravely tried to retake the cockpit. Authorities believe it was headed for the White House.

The hijackings were part of a coordinated attack. In all, 2,977 people lost their lives—574 more than the number who died in Japan’s assault on Pearl Harbor during World War II (1939-45). But the damage went far beyond the death toll, and 25 years later, the world remains a vastly different place than it was before the day that became known as 9/11.

“There was a profound loss of innocence and shock that we could be attacked that way. It really shattered our sense of security as a nation,” says Jon Alterman of the Center for Strategic and International Studies, in Washington, D.C. It was also deeply disorienting for the rest of the globe to see the U.S. attacked so brazenly, he says. “There was a remarkable expression of solidarity from countries around the world.”

At 8:46 a.m. on September 11, 2001, Carlos Williams was running late. He was rushing down the street toward Stuyvesant High School in New York City. He had just started ninth grade a few days earlier. Suddenly, a huge airplane flew low overhead. A few blocks away it smashed into the upper floors of the North Tower of the World Trade Center.

“I felt the heat from that explosion,” says Williams, now 39. “It was a moment of disbelief.”

Williams didn’t know what he had just seen. He hurried into his school as fire trucks and police cars raced toward the burning building. On the ninth floor, students in his English class leaned against the windows. They were trying to see what was happening outside.

Williams and his classmates had witnessed the start of the deadliest foreign attack on United States soil.

On that day, 19 terrorists hijacked four commercial planes. The planes were turned into airborne weapons. The men flew two jets full of passengers into New York’s 110-story-tall Twin Towers. The buildings caught fire and collapsed. Thousands of people were trapped inside.

Seventeen minutes after the first plane hit, the second plane crashed into the South Tower at 9:03 a.m. Thirty-four minutes later, hijackers flew a third plane that had been heading from Virginia to Los Angeles into the Pentagon. The Department of Defense headquarters is located outside Washington, D.C. A fourth plane, known as United Flight 93, crashed shortly afterward in rural Pennsylvania. It was brought down by passengers who bravely tried to retake the cockpit. Authorities believe it was headed for the White House.

The hijackings were part of a planned attack. In all, 2,977 people lost their lives—574 more than the number who died in Japan’s assault on Pearl Harbor during World War II (1939-45). But the damage went far beyond the death toll. Twenty-five years later, the world remains a very different place than it was before the day that became known as 9/11.

“There was a profound loss of innocence and shock that we could be attacked that way. It really shattered our sense of security as a nation,” says Jon Alterman of the Center for Strategic and International Studies in Washington, D.C. It was also confusing for the rest of the globe to see the U.S. attacked so brazenly, he says. “There was a remarkable expression of solidarity from countries around the world.”

To most Americans, 9/11 appeared to come out of nowhere. The decade before had seemed relatively peaceful, and terrorism wasn’t something that overly concerned people in the U.S.

But in many Arab countries in the Middle East, resentment had been building among some who saw the U.S. as a corrupting influence over their religion, culture, and politics. They also viewed America’s support of its longtime ally Israel and the ongoing U.S. military presence in the region as a threat.

To most Americans, 9/11 appeared to come out of nowhere. The decade before had seemed relatively peaceful. People in the U.S. weren’t concerned about terrorism.

But in many Arab countries in the Middle East, resentment had been building. Some people saw the U.S. as a bad influence over their religion, culture, and politics. They also felt threatened by America’s support of its longtime ally Israel and the ongoing U.S. military presence in the region.

In the late 1980s, a Saudi Arabian-born militant named Osama bin Laden formed a terrorist group called Al Qaeda, which operated mainly in Afghanistan, Sudan, and Pakistan. Al Qaeda followed an extreme form of Islam that the vast majority of Muslims don’t agree with. The group insisted on using terrorism to punish Western countries, and the U.S. in particular, for their perceived crimes against Islam.

The U.S. government was aware of Al Qaeda before 9/11. In 1998, the group bombed two American embassies, in Tanzania and Kenya, and in 2000, a U.S. Navy ship in Yemen. But none of those attacks matched the scale and scope of 9/11, which Al Qaeda planned for years. Some of the hijackers even attended flight school in the U.S.

The terrorists targeted the Twin Towers because of what they represented. Located near Wall Street in the cultural and financial capital of the U.S., they symbolized America’s economic power. Now, on the morning of September 11, people around the world were glued to their TVs, watching in shock and disbelief as the towers spewed smoke and then toppled to the ground.

In the late 1980s, a Saudi Arabian-born militant named Osama bin Laden formed a terrorist group called Al Qaeda. The group mainly operated in Afghanistan, Sudan, and Pakistan. Al Qaeda followed an extreme form of Islam that the vast majority of Muslims don’t agree with. The group insisted on using terrorism to punish Western countries, especially the U.S., for their perceived crimes against Islam.

The U.S. government was aware of Al Qaeda before 9/11. In 1998, the group bombed two American embassies, in Tanzania and Kenya. A U.S. Navy ship in Yemen was bombed in 2000. But none of those attacks matched the scale and scope of 9/11, which Al Qaeda planned for years. Some of the hijackers even attended flight school in the U.S.

The terrorists targeted the Twin Towers because of what they represented. They symbolized America’s economic power. The buildings were located near Wall Street in the cultural and financial capital of the U.S. Now, on the morning of September 11, people around the world were glued to their TVs. People watched in disbelief as smoke poured out of the towers, and they later toppled to the ground.

Inside Stuyvesant High School, students tried to stay calm and figure out what was happening. At first, they thought maybe it had been an accident. It wasn’t until the second plane hit that they realized the city was under attack.

A little more than an hour after the first plane had struck, the South Tower collapsed, sending a huge dust cloud rushing toward the school, where the lights flickered off and the building shook. Williams and his classmates evacuated about 30 minutes later, just as the North Tower came crashing down.

On the ground in New York City, chaos reigned. Public transportation shut down. Cell networks were jammed with desperate people trying to make calls. Williams lived about 5 miles away, in Brooklyn, and he couldn’t reach his mother. So he stuck with a couple of kids from his homeroom, and together they joined the throngs of people—many of them covered with ash—walking north, away from the catastrophe at what would soon become known around the world as Ground Zero.

“We kept looking back, and the giant cloud of dust and debris seemed to be moving north, chasing us,” Williams recalls.

The rubble of the World Trade Center smoldered for months, covering lower Manhattan in a toxic haze. But from those ashes also arose a great outpouring of national unity. People across the country put up American flags in their front yards, and the nightly news told stories of incredible acts of heroism. There were office workers who had carried injured colleagues down smoke-filled stairwells and first responders who had charged into the burning buildings, risking their lives—and in many cases losing them—to save others.

However, for many Muslim Americans, Arab Americans, and immigrants, the aftermath of 9/11 was also marked by a troubling increase in racial profiling and hate crimes.

The political response, meanwhile, was swift. The day after 9/11, the North Atlantic Treaty Organization (NATO)—a defense pact among nations in Europe and North America—declared that the attack would be considered an attack on all 19 member countries. The other NATO nations all vowed to support the U.S. in its military response. It was the first, and remains the only, time NATO has ever invoked its mutual-defense guarantee.

Inside Stuyvesant High School, students tried to stay calm. They tried to figure out what was happening. At first, they thought maybe it had been an accident. It wasn’t until the second plane hit that they realized it was an attack.

A little more than an hour after the first plane had struck the North Tower, the South Tower collapsed. A huge dust cloud rushed toward the school. The lights flickered off and the building shook. Williams and his classmates evacuated about 30 minutes later, just as the North Tower came crashing down.

On the ground in New York City, it was chaos. Public transportation shut down. Cell networks were jammed with desperate people trying to make calls. Williams lived about 5 miles away, in Brooklyn. He couldn’t reach his mother. He stuck with a couple of kids from his homeroom, and they joined crowds of people walking north. Many were covered with ash. They walked away from the catastrophe at what would soon become known around the world as Ground Zero.

“We kept looking back, and the giant cloud of dust and debris seemed to be moving north, chasing us,” Williams recalls.

The rubble of the World Trade Center smoldered for months. It covered lower Manhattan in a toxic haze. But from those ashes also arose a great outpouring of national unity. People across the country put up American flags in their front yards. The nightly news told stories of incredible acts of heroism. Office workers had carried injured colleagues down smoke-filled stairwells. First responders had charged into the burning buildings, risking their lives—and in many cases losing them—to save others.

However, for many Muslim Americans, Arab Americans, and immigrants, the aftermath of 9/11 saw an increase in racial profiling and hate crimes.

The political response, meanwhile, was quick. The day after 9/11, the North Atlantic Treaty Organization (NATO)—a defense pact among nations in Europe and North America—declared that the attack would be considered an attack on all 19 member countries. The other NATO nations all vowed to support the U.S. in its military response. It was the first, and remains the only, time NATO has ever invoked its mutual-defense guarantee.

On September 14, President George W. Bush visited Ground Zero. As he stood atop a pile of rubble and spoke into a megaphone, rescue workers called out, “We can’t hear you!”

“I can hear you! The rest of the world hears you,” Bush yelled back. “And the people who knocked these buildings down will hear all of us soon.”

Bush’s “bullhorn address” essentially kicked off what became known as the War on Terror. A month later, American troops invaded Afghanistan to topple the Taliban, an extremist religious group that controlled most of the country and had been harboring Bin Laden when he planned the attack.

Then in 2003, a U.S.-led coalition invaded Iraq. Bush portrayed the war as part of the larger fight against terror, since officials believed Iraq’s leader, Saddam Hussein, had hidden weapons of mass destruction, though none were ever found. In 2011, U.S. commandos killed Bin Laden in Pakistan, where he had been hiding.

On September 14, President George W. Bush visited Ground Zero. He stood atop a pile of rubble and spoke into a megaphone. Rescue workers called out, “We can’t hear you!”

“I can hear you! The rest of the world hears you,” Bush yelled back. “And the people who knocked these buildings down will hear all of us soon.”

Bush’s “bullhorn address” essentially kicked off what became known as the War on Terror. A month later, American troops invaded Afghanistan with the goal of toppling the Taliban. The extremist religious group controlled most of the country and had been protecting Bin Laden when he planned the attack.

Then in 2003, a U.S.-led coalition invaded Iraq. Bush portrayed the war as part of the larger fight against terrorism. Officials believed Iraq’s leader, Saddam Hussein, had hidden weapons of mass destruction, but none were ever found. In 2011, U.S. commandos killed Bin Laden in Pakistan, where he had been hiding.

Both wars have had enduring consequences. The Iraq War lasted more than eight years. The war in Afghanistan dragged on for 20 years and became the longest in U.S. history. More than 7,000 American troops died in the two conflicts, and more than 53,000 were wounded. The combined cost of the War on Terror is $8 trillion so far, according to Brown University’s Costs of War project.

Despite the massive expense, neither the Iraq nor the Afghanistan war succeeded in eliminating the root causes of terrorism in those countries or in stabilizing the region. In fact, new terrorist groups, such as the Islamic State, emerged amid the long-term chaos of the fighting. The vast number of civilians killed in the regional violence—more than 430,000, according to the Costs of War project—aggravated tensions and stoked anti-American feelings. And in Afghanistan, the Taliban retook control of the country as soon as the U.S. withdrew all its troops in 2021.

“America’s standing in the Middle East and the broader Islamic world suffered irreparably as a result of the wars and has never really recovered,” says Michael O’Hanlon, a national security expert at the Brookings Institution, a public policy research organization.

Both wars have had enduring consequences. The Iraq War lasted more than eight years. The war in Afghanistan dragged on for 20 years. It became the longest in U.S. history. More than 7,000 American troops died in the two conflicts, and more than 53,000 were wounded. The combined cost of the War on Terror is $8 trillion so far, according to Brown University’s Costs of War project.

Neither the Iraq nor the Afghanistan war succeeded in eliminating the root causes of terrorism or in stabilizing the region. In fact, new terrorist groups, such as the Islamic State, emerged. The vast number of civilians killed in the violence—more than 430,000, according to the Costs of War project—aggravated tensions and stoked anti-American feelings. And in Afghanistan, the Taliban retook control of the country as soon as the U.S. withdrew all its troops in 2021.

“America’s standing in the Middle East and the broader Islamic world suffered irreparably as a result of the wars and has never really recovered,” says Michael O’Hanlon, a national security expert at the Brookings Institution, a public policy research organization.

The 9/11 attacks also changed how Americans live (see “After 9/11,” below). The Patriot Act, which President Bush signed into law less than two months later, bolstered the government’s ability to monitor Americans’ communications. In 2002, Congress created a new agency called the Department of Homeland Security and put in place new procedures and laws that gave the government more power to protect against future terrorist attacks. The newly formed Transportation Security Administration (T.S.A.) beefed up and standardized airport security procedures, and the screenings Americans routinely pass through today in order to board planes are one of the most recognizable effects of the post-9/11 world.

Many nations in Europe and Asia have enacted similar changes. It’s become commonplace to pass through metal detectors to enter government buildings or sports arenas, to see armed soldiers patrolling airports and train stations, and to be recorded by surveillance cameras that monitor city streets.

“There’s a level of security that we take for granted now that we never had before,” says Alterman of the Center for Strategic and International Studies.

Those changes have prompted an ongoing debate about whether the added security measures have come at the expense of civil liberties, especially our right to privacy. Still, in the 25 years since 9/11, there hasn’t been another successful large-scale attack on U.S. soil by a foreign terrorist organization, though individuals inspired by extreme ideologies have carried out smaller attacks.

What are the lessons of 9/11? As the vice president of education programs for the 9/11 Memorial & Museum, Megan Jones helps young people try to understand what happened and how we can learn from it. The attacks, she says, were a turning point that undermined Americans’ sense of being protected from the dangers of the wider world.

Despite all the ways life has changed since then, Jones says, the key lesson from 9/11 is still relevant.

“In those days after 9/11, people of all backgrounds came together to support each other,” she says. “People were put into situations that were unimaginable. We saw that ordinary people are capable of extraordinary things. And that’s still true.”

The 9/11 attacks also changed how Americans live (see “After 9/11,” below). President Bush signed the Patriot Act into law less than two months later. It strengthened the government’s ability to monitor Americans’ communications. In 2002, Congress created a new agency called the Department of Homeland Security. They also put into place new procedures and laws that gave the government more power to protect against future terrorist attacks. The newly formed Transportation Security Administration (T.S.A.) standardized and increased airport security procedures. The screenings Americans pass through today in order to board planes are among the most recognizable effects of the post-9/11 world.

Many nations in Europe and Asia have enacted similar changes. It’s become commonplace to pass through metal detectors to enter government buildings or sports arenas and to see armed soldiers patrolling airports and train stations. Surveillance cameras record and monitor city streets.

“There’s a level of security that we take for granted now that we never had before,” says Alterman of the Center for Strategic and International Studies.

Those changes have prompted an ongoing debate about whether the added security measures have come at the expense of our right to privacy. Still, in the 25 years since 9/11, there hasn’t been another successful large-scale attack on U.S. soil by a foreign terrorist organization. Individuals inspired by extreme ideologies have carried out smaller attacks.

What are the lessons of 9/11? As the vice president of education programs for the 9/11 Memorial & Museum, Megan Jones helps young people try to understand what happened and how we can learn from it. The attacks, she says, were a turning point that damaged Americans’ sense of being protected from the dangers of the wider world.

Despite all the ways life has changed since then, Jones says, the key lesson from 9/11 is still relevant.

“In those days after 9/11, people of all backgrounds came together to support each other,” she says. “People were put into situations that were unimaginable. We saw that ordinary people are capable of extraordinary things. And that’s still true.”