The terrorist attacks of September 11, 2001 were a series of suicide attacks against the United States coordinated by the Islamist organization al-Qaeda. On that morning, nineteen terrorists hijacked four commercial passenger aircraft. The hijackers intentionally crashed two of the airliners into the Twin Towers of the business complex World Trade Center in New York City, killing everyone on board and many of the people working in the buildings. Both buildings collapsed two hours after the impact, destroying nearby buildings and causing a number of other damage. The third airliner crashed into the Pentagon, headquarters of the U.S. Department of Defense in Arlington County, Virginia, just outside Washington, DC. The fourth plane crashed in an open field near Shanksville, Pennsylvania, after some of its passengers and crew have tried to regain control of the aircraft from the kidnappers, who had redirected toward the U.S. capital. There were no survivors in any of the flights.
Nearly three thousand people died during the attacks, including 227 civilians and 19 hijackers on board the planes. The overwhelming majority of casualties were civilians, including nationals of over 70 countries.
The United States responded to the attacks by launching the War on Terror: the country invaded Afghanistan to overthrow the Taliban, who harbored the terrorists of al-Qaeda. The United States also passed the USA PATRIOT Act. Many other countries also strengthened their anti-terrorism legislation and expanded the powers of law enforcement. Some American stock exchanges stayed closed for the rest of the week following the attack and posted enormous losses reopening, especially in the airline and insurance industries. The disappearance of billions of dollars in destroyed offices caused serious damage to the economy of Lower Manhattan, in New York.
The damage to the Pentagon was repaired within a year, and the Pentagon Memorial was built adjacent to the building. The rebuilding process has started on the World Trade Center. In 2006, a new office tower was completed on site, the World Trade Center. Tower One World Trade Center is under construction on site, with 541 meters tall upon completion, will be one of the tallest skyscrapers in North America. Three more buildings are planned to be built on the site of the former Twin Towers, and a memorial to the victims of the attacks already completed. The Flight 93 National Memorial was begun November 8, 2009 and the first phase of construction was completed on the 10th anniversary of the September 11 attacks in 2011.