White Southerners founded the Confederacy on the ideology of white supremacy. Confederate soldiers on their way to Antietam and Gettysburg, their two main forays into Union states, put this ideology into practice: they seized scores of free black people in Maryland and Pennsylvania and sold them south into slavery. Confederates maltreated black Union troops when they captured them.

The American Civil War (ACW), also known as the War of the Rebellion, the Great Rebellion, and several other names, was a civil war that was fought in the United States of America from 1861 to 1865. Fearing that the future of slavery was in jeopardy after the election of an anti-slavery U.S. president, eleven slave-holding U.S. states located in the southern United States declared their secession from the country and formed the Confederate States, also known as "the Confederacy", sparking war. Led by Democrat Jefferson Davis, they fought against the United States, also known as "the Union", led by Republican Abraham Lincoln, which consisted of every free U.S. state as well as five slave-holding states, known as "border states". In 1865, after four years of warfare, the Confederacy surrendered, and slavery was abolished in the United States with the ratification of the Thirteenth Amendment to the United States Constitution by three-fourths of the states.