The date of September 11th primarily refers to the series of four coordinated terrorist attacks by the Islamic extremist group al-Qaeda against the United States on the morning of Tuesday, September 11, 2001. These events are commonly known as the September 11 attacks or 9/11. The attacks involved the hijacking of four commercial airliners by 19 al-Qaeda terrorists.
The sequence of events on that day involved two hijacked planes, American Airlines Flight 11 and United Airlines Flight 175, being crashed into the North and South Towers, respectively, of the World Trade Center complex in New York City, leading to the eventual collapse of both skyscrapers. A third plane, American Airlines Flight 77, was crashed into the Pentagon in Arlington, Virginia. The fourth plane, United Airlines Flight 93, crashed into a field in Shanksville, Pennsylvania, after its passengers and crew attempted to retake control from the hijackers. The attacks resulted in 2,977 fatalities, making it the single deadliest terrorist attack in human history.
The aftermath of the September 11 attacks had profound and lasting consequences on a global scale. It prompted the United States to launch the "War on Terror," which included the invasion of Afghanistan to depose the Taliban, who had harbored al-Qaeda. Domestically, it led to the creation of the Department of Homeland Security and the implementation of extensive new aviation and security legislation, such as the USA PATRIOT Act. The date is now observed in the United States as Patriot Day, a national day of service and remembrance for the victims.
