The American Civil War was a war fought in the United States from 1862 to 1865. The war was fought between the North (the Union) and the South (the Confederacy) primarily due to the controversy over the enslavement of black people.
In February 1861, seven slave states of the South seceded from the country and organized the Confederate States of America. A total of 13 states joined the Confederate States. War broke out in April of 1861 when secessionist forces of the Confederate States attacked Fort Sumter.
At the end of the Civil War, the Thirteenth Amendment to the United States Constitution abolished slavery throughout the United States.
Just before the Civil War, the United States had 34 total states, 19 of which were free states and 15 of which were slave states. A free state was a state in which slavery was either prohibited or being phased out. A slave state was one in which slavery was legal.
Free states were generally located in the Union, and slave states were located in the Confederacy. The Mason-Dixon line was a boundary between Maryland and Pennsylvania that served as a dividing line between the slave states and the free states. At this time, however, there were also territories in the western United States that didn’t necessarily follow the North-South divide when it came to slavery. Throughout the Civil War, some states become free states while some became free only at the end of the Civil War with the ratification of the Thirteenth Amendment.