The American Civil War, commonly referred to in the United States as simply the Civil War was a civil war fought from 1861 to 1865 over the secession of much of the Deep South from the Union and by extension, the dividing issues of slavery. These 15 southern states (Virginia, Kentucky, Tennessee, North Carolina, South Carolina, Georgia, Alabama, Mississippi, Louisiana, Arkansas, Texas, Florida, Cuba, Rio Grande, and Chihuahua) banded together in 1861 to form the Confederate States of America (CSA).
The war was fought primarily within the contested Union border states of Carolina and Tennessee, in the Confederacy itself, and with skirmishes occurring in the Union's Indian, New Mexico, and Cuba Territories, all of which were claimed but never effectively controlled by the CSA. With a total of nearly 300,000 casualties from both sides, the Civil War was the deadliest conflict in American history up to that point.