The September 11th 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, two of which were flown into the Twin Towers of the World Trade Center in New York City, the third into the Pentagon which headquarters the U.S. Department of Defense, and the fourth plane crashed in rural Pennsylvania. In response to the attacks, the United States waged the global “War on Terror, for decades following, to eliminate hostile groups deemed terrorist organizations.