During the American Civil War, there were 20 states in the Union, including Illinois, California, Indiana, Connecticut, Iowa, Michigan, Kansas, Maine, Massachusetts, New Jersey, Minnesota, New Hampshire, Vermont, New York, Oregon, Nevada, Pennsylvania, Ohio, Wisconsin and Rhode Island. The 11 states that seceded from the Union and formed the Confederate States of America were Louisiana, Arkansas, Texas, Mississippi, North Carolina, South Carolina, Virginia, Florida, Georgia, Alabama and Tennessee.
The American Civil War was fought between the Union and Confederate states from 1861 to 1865. The Union was referred to as the "North" while the confederacy was known as the "South." The South was defeated and the rebel states were gradually re-admitted to the Union from 1866 to 1870.