What major event happened on September 11, 2001?

The major event that occurred on September 11, 2001, was the terrorist attacks on the United States. On that day, a coordinated group of terrorists associated with the extremist group al-Qaeda hijacked four commercial airplanes. Two of these planes were flown into the Twin Towers of the World Trade Center in New York City, leading to the collapse of both towers. Another plane was directed at the Pentagon, while the fourth crashed into a field in Pennsylvania after passengers attempted to regain control from the hijackers. This tragic event resulted in the deaths of nearly 3,000 people and had significant global implications, leading to widespread changes in U.S. domestic and foreign policies, including the initiation of the War on Terror.

The other options refer to significant historical events but do not correlate with the date in question. For instance, the Revolution in Iraq refers to the U.S.-led invasion in 2003, the Paris Agreement was signed in 2016 as a framework to combat climate change, and the Cold War formally ended in the early 1990s with the dissolution of the Soviet Union. These events either occurred before or after September 11, 2001, highlighting the uniqueness and importance of that specific day in American history.