American Civil War: Union soldiers find a copy of Robert E. Lee's battle plans in a field outside Frederick, Maryland. It is the prelude to the Battle of Antietam.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union to preserve slavery in the United States. The South saw slavery as threatened because of the election of Abraham Lincoln and the…