What is the bloodiest event in United States history, in terms of casualties?

The answer is the Battle of Antietam, fought on September 17, 1862, during the American Civil War. It is considered the bloodiest single-day battle in U.S. history, with an estimated total of around 23,000 casualties. The battle took place near Sharpsburg, Maryland, and involved both Union and Confederate forces. The high number of casualties was primarily due to a series of intense and costly assaults throughout the day. The Battle of Antietam holds significance not only for its devastating loss of life but also because it marked a turning point in the Civil War, leading to key developments such as the Emancipation Proclamation.