9/11: The moment the world changed 20 years on | Under Investigation

September 11 attacks, also called 9/11 attacks, series of airline hijackings and suicide attacks committed in 2001 by 19 militants associated with the Islamic extremist group al-Qaeda against targets in the United States, the deadliest terrorist attacks on American soil in U.S. history. The attacks against New York City and Washington, D.C., caused extensive death and destruction and triggered an enormous U.S. effort to combat terrorism. Some 2,750 people were killed in New York, 184 at the Pentagon, and 40 in Pennsylvania (where one of the hijacked planes crashed after the passengers attempted to retake the plane); all 19 terrorists died (see Researcher’s Note: September 11 attacks). Police and fire departments in New York were especially hard-hit: hundreds had rushed to the scene of the attacks, and more than 400 police officers and firefighters were killed.