September 11 2001. World Trade Center Attacks

The September 11 attacks (also referred to as September 11, September 11th, or 9/11) were a series of four coordinated terrorist attacks launched by the Islamist terrorist group al-Qaeda upon the United States in New York City and the Washington, D.C. areas on September 11, 2001. On that Tuesday morning, 19 al-Qaeda terrorists hijacked four passenger jets, intending to fly them in suicide attacks into targeted buildings. Two of those planes, American Airlines Flight 11 and United Airlines Flight 175, were crashed into the North and South towers, respectively, of the World Trade Center complex in New York City. Both towers collapsed within two hours and falling debris, combined with fires that the debris initiated in several surrounding buildings, led to the partial or complete collapse of all the other buildings in the World Trade Center complex, also causing major damage to ten other large structures in the immediate area of the complex. A third plane, American Airlines Flight 77, was crashed into the Pentagon (the headquarters of the United States Department of Defense), leading to a partial collapse in its western side. The fourth plane, United Airlines Flight 93, was targeted at the United States Capitol in Washington, D.C., but crashed into a field near Shanksville, Pennsylvania after its passengers tried to overcome the hijackers. Almost 3,000 people died in the attacks, including all 227 civilians and 19 hijackers aboard the four planes.
Suspicion quickly fell on al-Qaeda, and in 2004, the group's leader, Osama bin Laden, who had initially denied involvement, claimed responsibility for the attacks. Al-Qaeda and bin Laden cited U.S. support of Israel, the presence of U.S. troops in Saudi Arabia, and sanctions against Iraq as motives for the attacks. The United States responded to the attacks by launching the War on Terror and invading Afghanistan to depose the Taliban, which had harbored al-Qaeda. Many countries strengthened their anti-terrorism legislation and expanded law enforcement powers. Having evaded capture for years, bin Laden was located and killed by U.S. forces in May 2011.

The north face of Two World Trade Center (south tower) immediately after being struck by United Airlines Flight 175

New One World Trade Center under construction on September 21, 2012

The destruction of the Twin Towers and other properties caused serious damage to the economy of Lower Manhattan and had a significant effect on global markets. Cleanup of the World Trade Center site was completed in May 2002, and the Pentagon was repaired within a year. Numerous memorials have been constructed, including the National September 11 Memorial & Museum in New York, the Pentagon Memorial, and the Flight 93 National Memorial in Pennsylvania. After a lengthy delay, the 1,776-foot-tall (541 m) One World Trade Center is expected to be completed at Ground Zero in New York City in 2013.