In the aftermath of Gettysburg, as the Army of Northern Virginia refitted and rested from its recent defeat. General Robert E. Lee and President Davis decided the fate of the Confederacy lays in the West as Army of Tennesse led by Bragg has been push out of Chattanooga and into northern Georgia. They decided to send Lieutenant General James Longstreet and six divisions by train to reinforce Bragg and the Army of Tennessee in north Georgia, where Federal General Rosecrans was threatening to push past the Confederates Army and into the heart of Georgia, much like what Sherman will eight months later.
By the morning of September 20, Longstreet and his six divisions were in position on the left flank of the Confederate line that had been established on the first day of the battle of Chickamauga. Longstreet mmediately began preparing to launch an attacks. After a delay in opening the attack, ultimately caused by Bragg, Lt Gen. Leonidas Polk and Daniel Harvey Hill. Longstreet's plan of attack wave finally moved forward at 11:10 a.m when Longstreet discovered that Bragg had ordered the right of Longstreet's line into action without consulting him. Rather than wasting time with details, he sent word to Hood to move the line forward. Its force was ferocious. Leading the attack across from the Brotherton farmhouse, General Hindman's front brigades encountered an extraordinary bit of luck. Owing to a mix-up in orders, Wood's Federals had left a hole in the Union line. Hindman wasted no time in pouring through this breach, laying waste to everything that came into his path. Within forty minutes, Longstreet's assault column destroyed two Federal Corps, leaving the survivors to run pell mell back to Chattanooga. Only Major General George Thomas' Corp remain on the field and they positioned themselve on the Snodgrass Hill. For some inexplicable reason, Bragg and rest of his command failed to pursue the retreating Union Corps or did they tried to dislodge Thomas from the Snodgrass. So Longstreet order his two divisions to assaults the Snodgrass Hill.As Longstreet began his push against the Federals due to lack of cooperation by Bragg and Polk as Polk's wing remained idle on the Confederate right, leaving Longstreet to assault the strong Federal position alone. Just them the Union reserve division under Granger that were stationed two miles away decided to march to the sound of battle, arriving just in time with 8000 men and fresh supply of ammunition to help out Thomas. As a result, Thomas and his quickly arranged defense were able to admirably hold off repeated Confederate assaults against Snodgrass. Granger and Thomas were able to hold off Longstreet's attack, thus, giving the Union Army much needed time to retreat.
Longstreet's memoirs indicate his extreme disappointment that a day so filled with success had failed to achieve results that had seemed so certain. He wrote that, "like magic the Union Army had melted away in our presence."