James Longstreet had years of military service by the time the Civil War broke out. After graduating from West Point in 1842, he fought in the Mexican War, and served in a variety of military posts throughout the west. When the Civil War began, he resigned from the United States Army to join the Confederacy.
Soon, he had risen to the upper ranks of the Army of Northern Virginia. He earned the trust of the army's commanding general, Robert E. Lee, who called Longstreet "my old war horse." He was instrumental to the Confederate victories in the Seven Days, Second Bull Run, and Fredericksburg. He coordinated many of the Confederate attacks during the defeat at Gettysburg. Despite his successes, Longstreet wanted an independent command of his own and requested a transfer to the western theater of the war. On September 5, 1863, Robert E. Lee and Confederate President Jefferson Davis agreed to send Longstreet with most of his corps to Tennessee to assist Braxton Bragg defending Chattanooga. In one of the most impressive logistical feats of the war, Longstreet moved most of his men west, where they began arriving in Ringgold, Georgia on September 17. By the final day of battle, Longstreet was in command of the entire left wing of Bragg's army, and his veterans of the Virginia campaigns were instrumental in breaking the Union center at Chickamauga.
After the victory at Chickamauga, Longstreet and his men participated in the siege of Chattanooga. But by this time disagreements between Longstreet and Bragg plagued the Confederate army. Longstreet left Chattanooga and moved towards Knoxville before rejoining the Army of Northern Virginia in the spring of 1864.
After the war, Longstreet became a Republican, the party associated with Abraham Lincoln and the Union army. He supported Ulysses S. Grant for the Presidency in 1868 and became reviled by many southerners as a "scalawag." In the Lost Cause mythology, many white southerners came to blame Longstreet for the failures of the Confederacy.