Tennessee is an interesting case in the Civil War. While it seceded and joined the Confederacy in the second wave of secession that followed Lincoln’s call for volunteers after the assault on Fort Sumter, its mountainous eastern region, with relatively few slaves, remained staunchly Unionist, and Andrew Johnson, who came from that area, refused to resign his U.S. Senate seat and would go on to serve as the state’s Unionist military governor, be elected Vice President of the United States in November 1864, and become President after Lincoln’s assassination in April 1865.
Andrew Johnson served as the anchor of Lincoln’s efforts to reconstruct the state during the war itself. That such a reconstruction could occur was all the more amazing since Tennessee was a battleground throughout the Civil War. With a number of highly strategic rivers (Cumberland, Mississippi, and Tennessee) touching its shores, natural invasion routes to the Deep South, the State of Tennessee became a natural location for Union and Confederate forces to clash over the course of the war. U.S. Grant would make his reputation in the state as a winning general taking Forts Henry and Donelson, before nearly losing it with a sanguinary victory at Shiloh in April 1862. Union forces would go on to capture Nashville and Memphis before year’s end, ironically leaving Unionist East Tennessee the only region of the state in the hands of the Confederacy. Union forces would challenge that control, only to be repulsed at Chickamauga in September 1863, retreating and being more-or-less besieged in Chattanooga, until U.S. Grant, fresh from his triumph at Vicksburg in Mississippi would return and drive the rebels from the state. The Confederates would belatedly return in Fall 1864, when John Bell Hood, in command of the rebel Army of Tennessee, after having been driven from Atlanta by William Tecumseh Sherman, tried to lure Sherman out of Georgia by invading Tennessee. Not to be sidetracked in his plans to march from Atlanta to the Atlantic Ocean, Sherman detailed part of his enormous force under George Thomas, to stop Hood, which Thomas did in two battles at Franklin and Nashville, where in the later engagement the Army of Tennessee was all but destroyed. With his victory at Nashville, Thomas secured Tennessee for the Union for all time.
Tennessee also had been the site of April 1864’s Fort Pillow Massacre, in which Confederate cavalry raiding the state under Nathan Bedford Forrest had overwhelmed a small garrison of African Americans and white Unionists manning an obscure fortification on the Mississippi River, and then slaughtered most of the black defenders, many after they tried to surrender.
Slavery in Tennessee, with its stronghold in the Mississippi Valley was undermined by the Union occupation of that region and Middle Tennessee, even though Abraham Lincoln, in an effort to bolster the state’s Unionists, exempted Tennessee from the Emancipation Proclamation. Seeing the hand-writing on the wall for slavery and with political ambitions beyond Tennessee, Andrew Johnson would call for “immediate” emancipation in Tennessee in late August 1863, although foreseeing a two-year legislative process to bring the peculiar institution to a final end in the state. Under pressure from Lincoln, who saw Tennessee as a test case for his administration’s ability to restore loyal state governments in South, and who by then believed slavery had to be eliminated as it was the root cause of secession, encouraged Johnson to speed up the process. So in January 1864, Johnson called a state constitutional convention to enact a reconstruction program for the state and require would-be voters to swear their support for an end to slavery in order to obtain suffrage. The convention was not held until a year later, after Johnson had been elected as Lincoln’s Vice President, and Tennessee voters approved the new state constitution in a vote on February 22, 1865, which included abolishing slavery. Tennessee became the third slave state and the first of the seceded states to end slavery on its own before the final ratification of the 13th Amendment. (Tennessee would ratify the 13th Amendment on April 5, 1865, the day the new state government took office.)
Source: Allen Carden, Freedom’s Delay: America’s Struggle for Emancipation, 1776-1865 (Knoxville: University of Tennessee Press, 2014), 280-81.