What significant event occurred in the US on September 11, 2001?

On September 11, 2001, a significant and tragic event occurred in the United States when terrorists attacked the country. This day is widely recognized due to a coordinated series of attacks carried out by the extremist group al-Qaeda. Four commercial airliners were hijacked, with two planes crashing into the Twin Towers of the World Trade Center in New York City and another crashing into the Pentagon in Arlington, Virginia. The fourth plane, United Airlines Flight 93, was headed for a target in Washington, D.C., but passengers attempted to retake control, and it ultimately crashed in Pennsylvania.

This event had far-reaching implications, leading to significant changes in U.S. domestic and foreign policy, heightened security measures, and the initiation of the War on Terror. The attacks resulted in the loss of nearly 3,000 lives and are remembered annually as a profound moment in American history, shaping national consciousness and international relations for years to come. Hence, this answer captures the essence of a pivotal moment that defined an era.