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

The major event that occurred in the United States on September 11, 2001, was a series of terrorist attacks. Coordinated by the extremist group al-Qaeda, these attacks involved the hijacking of four commercial airplanes. Two of these planes were flown into the Twin Towers of the World Trade Center in New York City, causing both towers to collapse. Another plane hit the Pentagon, the headquarters of the United States Department of Defense, while the fourth plane, United Airlines Flight 93, was headed for a target in Washington, D.C., but crashed into a field in Pennsylvania after passengers intervened.

The September 11 attacks had profound and lasting effects on U.S. domestic and foreign policies, leading to major changes in security protocols, military operations, and international relations. It prompted the United States to initiate the War on Terror, resulting in military interventions in Afghanistan and Iraq, and established the Department of Homeland Security to enhance national security.

The other possible answers do not align with the historical significance of September 11, 2001. While a nuclear attack would have been catastrophic, it did not occur. Similarly, there was no peace treaty signed on that day, nor did it mark an economic collapse, even though subsequent events following the attacks did