Two states joined the Union during the Civil War: West Virginia and Nevada.
- West Virginia separated from Virginia and was admitted to the Union on June 20, 1863, after residents of the western counties of Virginia opposed secession and chose to remain loyal to the Union
- Nevada was admitted to the Union during the war as well, in 1864, becoming a state that supported the Union cause
These additions increased the number of states in the Union during the conflict.
