The September 11 attacks, also known as 9/11, were a series of four coordinated terrorist strikes against the United States of America carried out by the militant Islamist terrorist group al-Qaeda on the morning of September 11, 2001.
On the morning, 19 al-Qaeda terrorists seized four commercial airplanes flying from the northeastern United States to California. Three groups of five hijackers and one group of four hijackers were formed. Each group had a hijacker who had completed flight instruction and assumed command of the plane. Their stated goal was for each plane to crash into a significant American building, resulting in mass casualties and partial or complete destruction of the targets.
American Airlines Flight 11 was the first plane to hit its target. At 8:46 a.m., it was flown into the World Trade Center’s North Tower in Lower Manhattan. United Airlines Flight 175 impacted the World Trade Center’s South Tower seventeen minutes later, at 9:03 a.m. Within an hour and 42 minutes, both 110-story towers collapsed, causing the fall of other World Trade Center structures, notably 7 World Trade Center, as well as major damage to nearby buildings.
A third jet, American Airlines Flight 77, was hijacked over Ohio after taking off from Dulles International Airport. It collided with the west side of the Pentagon (the American military’s headquarters) in Arlington County, Virginia, at 9:37 a.m., causing a partial collapse of the building’s side. United Airlines Flight 93, the fourth and last flight, was directed to Washington, D.C. At 10:03 a.m., this flight was the only one to miss its intended target, crashing in a field outside Shanksville, Pennsylvania. The passengers sought to wrest control of the jet from the hijackers, eventually diverting the flight away from its original destination. Flight 93’s intended target was either the White House or the United States Capitol, according to investigators.
Al-Qaeda was instantly singled out as a suspect in the aftermath of the assaults. The United States publicly responded by beginning the War on Terror and invading Afghanistan to remove the Taliban, who had refused to eject al-Qaeda from Afghanistan and extradite al-Qaeda leader Osama bin Laden, as demanded by the US. Despite originally denying any connection, bin Laden formally claimed credit for the bombings in 2004.  Al-Qaeda and bin Laden cited US support for Israel, US soldiers in Saudi Arabia, and sanctions against Iraq as reasons for their actions. Bin Laden was discovered in a bunker in Abbottabad, Pakistan, after eluding arrest for over a decade, and was killed during Operation Neptune Spear.
The demolition of the World Trade Center and nearby infrastructure devastated New York City’s economy and triggered a global economic downturn. To avoid terrorist attacks, many countries toughened their anti-terrorism legislation and enlarged the authority of law enforcement and intelligence organizations. The civilian airspaces of the United States and Canada were restricted until September 13, and Wall Street trade was halted until September 17. There were numerous closures, evacuations, and cancellations as a result of the attacks, either out of respect or fear of more attacks. In May 2002, the World Trade Center site was cleaned up, and the Pentagon was repaired a year later. The replacement of the World Trade Center complex began in November 2006, and the structure was completed in November 2014.
In addition to at least $10 billion in infrastructure and property damage, the attacks resulted in 2,977 deaths, over 25,000 injuries, and significant long-term health repercussions. With 340 and 72 died, it remains the deadliest terrorist assault in human history and the single deadliest incident for firefighters and law enforcement officials in the history of the United States. The National September 11 Memorial & Museum in New York City, the Pentagon Memorial in Arlington County, Virginia, and the Flight 93 National Memorial at the Pennsylvania crash site are just a few of the tributes that have been built.