The September 11 Terrorist Attacks 

The September 11 attacks (often referred to as simply 9/11) were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda against the United States on the morning of Tuesday, September 11, 2001. The attacks resulted in 2,977 fatalities, over 25,000 injuries, and substantial long-term health consequences, in addition to at least $10 billion in infrastructure and property damage. It was the single deadliest terrorist attack in human history and the deadliest incident for firefighters and law enforcement officers in American history, with 343 and 72 killed, respectively.

The origins of al-Qaeda can be traced to 1979 when the Soviet Union invaded Afghanistan. Osama bin Laden was Saudi Arabian and travelled to Afghanistan and helped to organize Arab resistance against the Soviets. He later objected to American foreign policy with respect to Israel and American troops in Saudi Arabia after the Gulf War. He grew more radical and called for a holy war against the United States

Early that morning, 19 al-Qaeda terrorists boarded four planes at three different airports: Logan Airport in Boston, Washington Dulles, and Newark Airport.  Two of the planes, American Airlines Flight 11 and United Airlines Flight 175, were deliberately crashed by the terrorists into the North and South towers of the World Trade Center complex in New York.

Within an hour and 42 minutes, both 110-story towers collapsed. Debris and the resulting fires caused a partial or complete collapse of all other buildings in the World Trade Center complex, as well as significant damage to 10 other large surrounding structures.

A third plane, American Airlines Flight 77, was crashed into the Pentagon (the headquarters of the U.S. Department of Defense) in Arlington County, Virginia, which led to a partial collapse of the building's west side. The fourth plane, United Airlines Flight 93, was initially flown toward Washington, D.C., but crashed into a field in Stonycreek Township, Pennsylvania, after a group of passengers on the plane heard about the other attacks from phones on the plane and fought back against the hijackers.

Suspicion quickly fell onto al-Qaeda. The United States responded by launching the War on Terror and invading Afghanistan to depose the Taliban, which had failed to comply with American demands to expel al-Qaeda from Afghanistan and extradite their leader Osama bin Laden. Many countries strengthened their anti-terrorism legislation and expanded the powers of law enforcement and intelligence agencies to prevent terrorist attacks. Although bin Laden initially denied any involvement, in 2004 he 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. After evading capture for almost a decade, bin Laden was located in Pakistan in 2011 and killed during a U.S. military raid.

One of the most controversial aspects of America's response was the Patriot Act, an Act of Congress that was signed into law by President George W. Bush in October 2001. The Patriot Act was an effort to dramatically tighten national security by expanding law enforcement's ability to conduct surveillance. Critics argued that this was rushed into law and a violation of civil liberties. 

The destruction of the World Trade Center seriously harmed the economy of New York City and had a significant effect on global markets. Wall Street was closed until September 17, and the U.S. and Canadian civilian airspaces until September 13. Many closings, evacuations, and cancellations followed, out of respect or fear of further attacks. Cleanup of the World Trade Center site was completed in May 2002, and the Pentagon was repaired within a year. The construction of One World Trade Center began in November 2006, and the building opened in November 2014. Numerous memorials have been constructed, including 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.

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