American Civil War

https://www.britannica.com/event/American-Civil-War
In 1861-1865: American Civil War, also called War Between the States, four-year war (1861–65) between the United States and 11 Southern states that seceded from the Union and formed the Confederate States of America.

The secession of the Southern states (in chronological order, South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, Tennessee, and North Carolina) in 1860–61 and the ensuing outbreak of armed hostilities were the culmination of decades of growing sectional friction over slavery. Between 1815 and 1861 the economy of the Northern states was rapidly modernizing and diversifying.

The civil war was fought between the United States and the 11 southern states, historically over slavery and the treatment of the negro race.