Until I have time to write my own description of the role of Tennessee in the Civil War I’m going to excerpt a section from the article on Wikipedia (accessed 8/2/10).
To a large extent, the American Civil War was fought in cities and farms of Tennessee; only Virginia saw more battles. Tennessee was the last of the Southern states to declare secession from the Union, but saw more than its share of the devastation resulting from years of warring armies criss-crossing the state. Its rivers were key arteries to the Deep South, and, from the early days of the war, Union efforts focused on securing control of those transportation routes, as well as major roads and mountain passes such as the Cumberland Gap.
A large number of important battles occurred in Tennessee, including the vicious fighting at the Battle of Shiloh, which at the time, was the deadliest battle in American history (it was later surpassed by a number of other engagements). Other large battles in Tennessee included Stones River, Chattanooga, Nashville, and Franklin.
Although the state became a part of the Confederacy, pockets of strong pro-Union sentiments remained throughout the war, particularly in the mountains in East Tennessee. The Vice President of the United States, Andrew Johnson, was a loyalist, as were a number of congressmen and state politicians. On the Confederate side, significant leaders included noted cavalryman Nathan B. Forrest and corps commanders Leonidas Polk and Benjamin F. Cheatham, as well as Governor Isham Harris.