What major event occurred in the United States on September 11, 2001?

The major event that occurred on September 11, 2001, was the terrorist attacks on the World Trade Center and the Pentagon. On that day, 19 terrorists hijacked four commercial airplanes, crashing two into the Twin Towers of the World Trade Center in New York City and another 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, leading it to crash in a Pennsylvania field instead.

This tragic event had profound and lasting impacts on U.S. domestic and foreign policy, leading to the War on Terror, changes in immigration and security policies, and reshaping global geopolitical dynamics. The attacks resulted in significant loss of life and prompted widespread national and international responses, including increased security measures and military operations in Afghanistan.

Other options refer to events that did not occur on that date. A natural disaster is not associated with September 11, 2001, nor did the bombing of Pearl Harbor take place then—it happened on December 7, 1941. An economic recession occurred later, but it is not directly linked to the events of that day.