Battle of Chickamauga

The army was formed on November 20, 1862, renaming the Army of Mississippi. Its first commander was General Braxton Bragg, who fought Union Maj. Gen. William Rosecrans's Army of the Cumberland to a draw at the Battle of Stones River on December 31, 1862. However, Bragg was forced to withdraw from Murfreesboro and fall back on Tullahoma.

In the summer of 1863, Rosecrans began an offensive, generally known as the Tullahoma Campaign, after the Confederate headquarters. Union forces gradually forced Bragg to fall back into northern Georgia, abandoning the important railroad hub of Chattanooga. However, reinforced by Lt. Gen. James Longstreet's corps from the Army of Northern Virginia, the Army of Tennessee was able to inflict a significant defeat on Rosecrans at Chickamauga in September 1863, advancing to besiege Chattanooga. The Army of the Cumberland was, however, reinforced by the troops of Maj. Gen. Ulysses S. Grant's Army of the Tennessee, along with two corps from the Army of the Potomac under Maj. Gen. Joseph Hooker, which combined with the Army of the Cumberland to inflict a significant defeat on Bragg at the Battle of Missionary Ridge on November 25, forcing Bragg to abandon the siege of Chattanooga and withdraw again into northern Georgia.

Shortly thereafter, Bragg was dismissed and replaced as commander of the army by Gen. Joseph E. Johnston, who was much better liked by both troops and high level subordinates than the sour Bragg. In the 1864 Atlanta Campaign, Johnston faced the combined Northern armies of Maj. Gen. William T. Sherman, whose orders were to destroy the Army of Tennessee, with the capture of Atlanta as the secondary objective. Johnston, who felt the continued existence of his army was more important than protecting territory, tended to avoid battle with Sherman, executing a skillful withdrawal, which caused impatience among the Confederate leadership in Richmond, particularly Confederate President Jefferson Davis, who had never gotten on well with Johnston. Following Sherman's outflanking of Johnston at the Chattahoochee River, forcing Johnston back on Atlanta itself, Johnston was replaced by Lt. Gen. John Bell Hood.

Hood's tenure as commander proved disastrous. After several unsuccessful attempts to force Sherman's withdrawal from Atlanta, the city fell to Union troops on September 2, 1864. Instead of continuing to parry against Sherman's forces, Hood now turned west and headed back north into Tennessee, allowing Sherman to turn south unopposed for the March to the Sea. In the meantime, Hood was faced in Tennessee by the army's old enemy, the Army of the Cumberland, under Maj. Gen. George H. Thomas, as well as the Army of the Ohio under Maj. Gen. John Schofield. On November 30, 1864, Hood attacked Schofield's smaller army at the Battle of Franklin, losing almost a quarter of his troops, but continued to advance north into central Tennessee, where he attempted to besiege Nashville. On December 15, Thomas's troops launched their attack, completely routing the Confederates in the most decisive tactical engagement of the war. The Federals pursued the retreating Army of Tennessee, which left stragglers, cannon, and small arms its wake. When the army stopped its retreat in Tupelo just before the new year, barely half of the men remained who had set out at the beginning of the campaign.

Thereafter, the Army of Tennessee ceased to be an effective fighting force, although its remnants were sent to the Carolinas to provide some opposition to Sherman's continuing advance in that area. The army surrendered to Sherman on April 26, 1865.

The name Army of Northern Virginia referred to its primary area of operation, as did most Confederate States Army names. The Army originated as the (Confederate) Army of the Potomac, which was organized on June 20, 1861, from all operational forces in northern Virginia. On July 20 and July 21, the Army of the Shenandoah and forces from the District of Harpers Ferry were added. Units from the Army of the Northwest were merged into the Army of the Potomac between March 14 and May 17, 1862. The Army of the Potomac was renamed Army of Northern Virginia on March 14. The Army of the Peninsula was merged in April 12, 1862.

Robert E. Lee's biographer, Douglas S. Freeman, asserts that the army received its final name from Lee when he issued orders assuming command on June 1, 1862. However, Freeman does admit that Lee corresponded with Joseph E. Johnston, his predecessor in army command, prior to that date and referred to Johnston's command as the Army of Northern Virginia. Part of the confusion results from the fact that Johnston commanded the Department of Northern Virginia (as of October 22, 1861) and the name Army of Northern Virginia can be seen as an informal consequence of its parent department's name. Jefferson Davis and Johnston did not adopt the name, but it is clear that the organization of units as of March 14 was the same organization that Lee received on June 1, and thus it is generally referred to today as the Army of Northern Virginia, even if that is correct only in retrospect.

In addition to Virginians, it included regiments from all over the Confederacy, even those as far away as Texas and Arkansas. Militiamen from the New Mexico and Arizona territories also served among its members.