What date marks the largest terrorist attack in U.S. history?

The date that signifies the largest terrorist attack in U.S. history is September 11, 2001. On this day, a coordinated series of attacks orchestrated by the terrorist group al-Qaeda resulted in the hijacking of four commercial airplanes. Two of those planes were flown into the Twin Towers of the World Trade Center in New York City, leading to the collapse of both towers, while another plane struck the Pentagon, and a fourth plane, United Airlines Flight 93, crashed in Pennsylvania after passengers attempted to regain control from the hijackers.

This tragic day resulted in nearly 3,000 deaths and significant destruction, profoundly impacting national security policies and leading to the onset of the War on Terror. The repercussions of the events of September 11 continue to influence U.S. domestic and foreign policy today, marking it as a pivotal moment in American history.

Other dates provided do not correspond to significant terrorist attacks of that magnitude, as September 11 stands alone as the most devastating attack on American soil. The events that transpired on that day defined a new era of global security concerns and responses to terrorism.