Tennessee seceded from the Union during the American Civil War. Initially, the state was divided on the issue of secession, but after the Confederate attack on Fort Sumter in April 1861 and President Abraham Lincoln's call for troops, public opinion shifted. On June 8, 1861, Tennessee officially voted to leave the Union and join the Confederacy, becoming the last Southern state to do so.

The state played a major role in the war, serving as a key battleground due to its strategic location and transportation routes. Tennessee saw more military engagements than any state except Virginia. While the western and middle parts of the state largely supported secession, many in East Tennessee remained loyal to the Union.

After the war, Tennessee was the first former Confederate state to be readmitted to the Union, in July 1866.