East Tennessee is one of the three Grand Divisions of Tennessee defined in state law. Geographically and socioculturally distinct, it comprises approximately the eastern third of the U.S. state of Tennessee. East Tennessee consists of 33 counties, 30 located within the Eastern Time Zone and three counties in the Central Time Zone, namely Bledsoe, Cumberland, and Marion. East Tennessee is entirely located within the Appalachian Mountains, although the landforms range from densely forested 6,000-foot (1,800 m) mountains to broad river valleys. The region contains the major cities of Knoxville and Chattanooga, Tennessee's third and fourth largest cities, respectively, and the Tri-Cities, the state's sixth largest population center.
During the American Civil War, most East Tennesseans remained loyal to the Union even as the state seceded and joined the Confederacy. Early in the war Unionist delegates unsuccessfully attempted to split East Tennessee into a separate state that would remain a part of the Union. After the war, a number of industrial operations were established in cities in the region. The Tennessee Valley Authority (TVA), created by Congress during the Great Depression, spurred economic development and helped to modernize the region's economy and society. Today, TVA's administrative operations are headquartered in Knoxville and its power operations are based in Chattanooga. Oak Ridge was the site of the world's first successful uranium enrichment operations which were used to construct the world's first atomic bombs, two of which were dropped on Imperial Japan at the end of World War II. The Appalachian Regional Commission further transformed the region in the latter 20th century.
East Tennessee is both geographically and culturally part of Appalachia, and has been included— along with Western North Carolina, North Georgia, Eastern Kentucky, Southwest Virginia, the state of West Virginia, western Maryland, and southwestern Pennsylvania — in every major definition of the Appalachian region since the early 20th century. East Tennessee is home to the nation's most visited national park— the Great Smoky Mountains National Park— and hundreds of smaller recreational areas. East Tennessee is often considered the birthplace of country music, due largely to the 1927 Victor recording sessions in Bristol, and throughout the 20th and 21st centuries has produced a steady stream of musicians of national and international fame.