The September 11 attacks, a series of coordinated terrorist attacks killing 2,977 people using four aircraft hijacked by 19 members of al-Qaeda. Two aircraft crash into the World Trade Center in New York City, a third crashes into The Pentagon in Arlington County, Virginia, and a fourth into a field near Shanksville, Pennsylvania.

The September 11 attacks, also known as 9/11, were four coordinated Islamist terrorist suicide attacks by al-Qaeda against the United States in 2001. Nineteen terrorists hijacked four commercial airliners, crashing the first two into the Twin Towers of the World Trade Center in New York City and the third into the Pentagon in Arlington County, Virginia. The fourth plane crashed in a rural Pennsylvania field during a passenger revolt. The attacks killed 2,977 people, making it the deadliest terrorist attack in history. In response to the attacks, the United States waged the global war on terror over multiple decades to eliminate hostile groups deemed terrorist organizations, as well as the governments purported to support them.

Al-Qaeda, is a pan-Islamist militant organization led by Sunni jihadists who self-identify as a vanguard spearheading a global Islamist revolution to unite the Muslim world under a supra-national Islamic caliphate. Its membership is mostly composed of Arabs but also includes people from other ethnic groups. Al-Qaeda has mounted attacks on civilian, economic and military targets of the U.S. and its allies; such as the 1998 US embassy bombings, the USS Cole bombing, and the September 11 attacks.

The original World Trade Center (WTC) was a complex of seven buildings in the Financial District of Lower Manhattan in New York City. Built primarily between 1966 and 1975, it was dedicated on April 4, 1973, and was destroyed during the September 11 attacks in 2001. At the time of their completion, the 110-story-tall Twin Towers, including the original 1 World Trade Center at 1,368 feet (417 m), and 2 World Trade Center at 1,362 feet (415.1 m), were the tallest buildings in the world; they were also the tallest twin skyscrapers in the world until 1996, when the Petronas Towers opened in Kuala Lumpur, Malaysia. Other buildings in the complex included the Marriott World Trade Center (3 WTC), 4 WTC, 5 WTC, 6 WTC, and 7 WTC. The complex contained 13,400,000 square feet (1,240,000 m²) of office space and, prior to its completion, was projected to accommodate an estimated 130,000 people.