On September 11, 2001, the United States experienced a series of coordinated terrorist attacks carried out by al-Qaeda, a militant group based in Afghanistan. The attacks involved hijacking four commercial airplanes, two of which crashed into the Twin Towers of the World Trade Center in New York City, one into the Pentagon in Washington, D.C., and one crashed in a field in Pennsylvania after passengers attempted to regain control of the plane. The attacks resulted in the deaths of nearly 3,000 people, making it the deadliest terrorist attack in human history. The events of 9/11 had a profound impact on the United States and the world, leading to significant changes in security measures, international relations, and the global fight against terrorism.