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

The event that took place on September 11, 2001, was the 9/11 terrorist attacks, which had a profound impact on the United States and the world. On that day, a coordinated group of terrorists from the extremist group al-Qaeda hijacked four commercial airplanes. They crashed two of these planes into the World Trade Center towers in New York City, causing both towers to collapse, while a third plane struck the Pentagon, the headquarters of the United States Department of Defense, located in Arlington, Virginia. The fourth plane, United Airlines Flight 93, was headed for a target in Washington, D.C., but passengers attempted to regain control, and it ultimately crashed in Pennsylvania.

The significance of 9/11 extends beyond the immediate destruction and loss of life; it represented a shift in U.S. domestic and foreign policy, leading to the wars in Afghanistan and Iraq, heightened security measures at home, and the establishment of the Department of Homeland Security. The event reshaped public perception and policy on terrorism and international relations.

In contrast, the other options refer to historically significant events but are unrelated to September 11, 2001. The Civil War occurred during the 19th century and involves a different context of American history,