What is the biggest tragedy in the US?

The biggest tragedy in the U.S. is often considered to be the September 11 attacks in 2001, which resulted in the deaths of nearly 3,000 people and had profound effects on national security, foreign policy, and societal attitudes towards terrorism. Other significant tragedies include the Civil War, which claimed hundreds of thousands of lives and deeply affected the nation's social fabric, and the ongoing impacts of systemic issues like racial violence and gun violence, which continue to claim lives and divide communities. Each of these events reflects deep societal fractures and has shaped the course of American history.