When reading about the movie Gangs of New York on wikipedia, i learned about the Battle of Antietam. In the movie a grown man returns to his town during the second year of the Civil war, on September 1862, days after the Battle of Antietam.
Picture taken from nps.gov
According to the US National Park Service, the Battle of Antietam, also known as the Battle of Sharpsburg, was held on September 17, 1862. It was the first major battle in the Civil War to take place in the North, and was also a part of the Maryland Campaign of 1862. After twelve hours of fierce fighting, on the 70,000 federal troops who have fought in the battle, 23,000 were killed and 35,000 Confederates lost the largest number of soldiers. The Battle of Antietam ended with the first invasion of the Confederate Army in Northern Virginia and led to the issuance of Abraham Lincoln’s preliminary Emancipation Proclamation.