September 11, 2001, also known as 9/11, was a tragic day in American history. On this day, a series of coordinated terrorist attacks were carried out by the extremist group Al-Qaeda on the United States. Four commercial airplanes were hijacked, with two of them crashing into the Twin Towers of the World Trade Center in New York City, causing both towers to collapse. Another plane crashed into the Pentagon in Arlington, Virginia, while the fourth plane, United Airlines Flight 93, crashed into a field in Pennsylvania after passengers attempted to regain control from the hijackers.

The attacks resulted in the deaths of nearly 3,000 people, including passengers and crew members on the planes, as well as individuals in the targeted buildings and emergency responders. It was the deadliest terrorist attack in world history and had a profound impact on global politics and security.

The events of September 11, 2001, led to significant changes in U.S. foreign and domestic policies. The U.S. launched the War on Terror, with a focus on combating terrorism and dismantling Al-Qaeda. The attacks also prompted the creation of the Department of Homeland Security and the implementation of stricter security measures at airports and other public places.

The memory of September 11, 2001, remains a somber reminder of the vulnerability of nations to acts of terrorism and the importance of international cooperation in preventing such attacks. The date is observed annually as a National Day of Service and Remembrance in the United States.