The Army of Tennessee, known by various names in the course of its existence, was the Confederacy's principal army on the western front. From the Appalachian Mountains to the Mississippi River, this force fought most of the major battles that took place in the region.

The army traced it origins to the early spring and summer of 1861, when Tennessee Governor Isham G. Harris spearheaded the effort to raise the Provisional Army of Tennessee. The army, one of the largest and best organized of the Southern forces, transferred to Confederate service in July 1861. Placed under the command of General Albert Sidney Johnston, it became the core of the Southern army in the Western Theater. In the opening days of the war, the army defended the northern frontier of the Confederacy along the Tennessee-Kentucky border before retreating following the Federal capture of Fort Henry and Fort Donelson on the Tennessee and Cumberland Rivers in February 1862.

The army concentrated at Corinth, Mississippi. General P. G. T. Beauregard, second in command, styled the forty-four-thousand-man force the "Army of the Mississippi." On April 6-7, 1862, this army engaged Union General Ulysses S. Grant's Army of the Tennessee in the battle of Shiloh, the first large-scale battle of the war. An apparent Confederate victory on the first day turned into defeat on the second. The army limped back to Corinth, having suffered more than ten thousand casualties, including the death of Johnston.

Although Beauregard succeeded to command of the army, his conflicts with President Jefferson Davis soon led to his replacement by General Braxton Bragg. For the next year and a half, Bragg led the army through some of the hardest marching and toughest fighting of the war. In November 1862, soon after the culmination of Bragg's first campaign at the battle of Perryville and the subsequent retreat into Tennessee, the army officially became known as the Army of Tennessee, the designation it carried for the rest of the war.

In the last days of December 1862, the thirty-eight-thousand-man Army of Tennessee took up a position thirty miles southeast of Nashville along the banks of the west fork of the Stones River near the small town of Murfreesboro. The Confederate forces faced a forty-four-thousand-man Union army under the command of General William S. Rosecrans. Both armies straddled the Nashville Turnpike and the railroad leading into that city.

Early on December 31, 1862, the Army of Tennessee struck the enemy's right flank and drove the Federals back to the turnpike and railroad. But the initial success could not be sustained. After three days of fighting, Bragg withdrew and the Federals claimed victory, although both sides suffered an almost equal number of casualties.

The Army of Tennessee held the Nashville and Chattanooga Railroad near Tullahoma for the next several months. In the summer of 1863 Rosecrans adroitly maneuvered Bragg's forces from their defensive position, sending them into retreat to North Georgia, just south of Chattanooga. Reinforcements from General James Longstreet's Virginia corps bolstered the Army of Tennessee. On September 19-20, the army attacked Rosecrans along the banks of Chickamauga Creek, fighting one of the fiercest engagements of the war. Confederate casualties numbered more than eighteen thousand, while the Union forces lost more than sixteen thousand men. Despite its losses, the battle became one of the Army of Tennessee's greatest tactical triumphs. The Southern forces drove the Union army back to Chattanooga; only the skillful action of General George Henry Thomas prevented the retreat from becoming a rout.

But Bragg failed to follow up his advantage. Criticism of the general, which had been mounting since the retreat from Kentucky and the battle of Stones River, reached new heights. Jefferson Davis visited the army and raised expectations that he would relieve Bragg of his command. Davis, however, decided to retain the general. Then, in late November 1863, Grant, who had replaced Rosecrans as Union commander, decisively defeated Bragg in the battles for Chattanooga, forcing him to withdraw to North Georgia and making the costly triumph at Chickamauga strategically worthless. Davis relieved Bragg of his command and named General Joseph E. Johnston to head the Army of Tennessee.

Johnston strengthened the army's morale and numbers, but faced an enormous task in the spring of 1864. General William T. Sherman, with superior numbers, launched his campaign to capture Atlanta. Gradually, Johnston fell back before Sherman's advance, presumably seeking an opening to strike the Union forces at an unguarded moment. Johnston found only one opportunity, and even then, General John Bell Hood, who had been expected to lead the attack, held back, fearing a Federal attack on his flank if he moved forward. The Confederates continued to retreat under pressure of Sherman's enveloping maneuvers.

A disenchanted Davis removed Johnston from command and gave command of the Army of Tennessee to Hood, who had been sending Davis criticisms of Johnston for continually retreating. Hood's engagements around Atlanta cost the army a terrible price in the numbers of dead and wounded, all to no avail. On September 2, 1864, Sherman captured Atlanta.

Hood then moved the Army of Tennessee northward, hoping to draw Sherman away from Georgia. Instead, Sherman headed for Savannah, leaving General Thomas to cope with Hood's forces in Tennessee. Crossing the Tennessee River and moving into Middle Tennessee, Hood led the Army of Tennessee into an ill-advised frontal assault at Franklin on November 30, 1864. This battle resulted in seven thousand casualties, including the deaths of six Confederate generals.

Nevertheless, Hood decided to move on to Nashville, where the army was decisively defeated on December 15-16, 1864. The remnants of the Army of Tennessee managed to reach safety on the Tennessee River, but Hood lost his command, and Johnston returned to lead the weakened, hard-luck army into the Carolinas, where they fought once more at Bentonville, before surrendering at Durham, North Carolina, in late April 1865. The Army of Tennessee gained a reputation as a tough, hard-marching, hard-fighting unit. Usually outnumbered and led by inept commanders, the Army of Tennessee nevertheless achieved an impressive record as a fighting force.