World Trade Center site
On the morning of September 11, 2001, Islamic terrorists affiliated with Al-Qaeda hijacked American Airlines Flight 11 and United Airlines Flight 175, both which were en route to Los Angeles, and intentionally crashed them into the two main towers of the World Trade Center. The towers collapsed within two hours of the collisions. 2,606 people, including 2,192 civilians, 71 law enforcement officers, and 343 firefighters, who were in the towers and in the surrounding area died in the attacks, as well as 147 civilians and the 10 hijackers aboard the two airliners. After the collapse of the World Trade Center, hospital workers and law enforcement officers began referring to the World Trade Center site as "Ground Zero".
Al-Qaeda
In December 1998, the Director of the CIA Counterterrorism Center reported to President Bill Clinton that al-Qaeda was preparing to launch attacks in the United States, and that the group was training personnel to hijack aircraft. On September 11, 2001, al-Qaeda attacked the United States, hijacking four airliners within the country and deliberately crashing two into the twin towers of the World Trade Center in New York City. The third plane crashed into the western side of the Pentagon in Arlington County, Virginia. The fourth plane was crashed into a field in Shanksville, Pennsylvania. In total, the attackers killed 2,977 victims and injured more than 6,000 others.