In two days of fighting in those woods, the two armies lost somewhere around 34,000 men, killed, wounded, and missing, making Chickamauga the second-bloodiest battle of the entire Civil War, behind only Gettysburg, fought ten weeks earlier. The most-cited tally puts the Union loss at about 16,170 and the Confederate at about 18,454. The side that won the field lost more men doing it than the side it drove off. The Confederates bled harder for their victory, nearly a fifth of the men they put in the field, than the Union did for its defeat.

The dense woods that had blinded the battle also made it uniquely cruel. Men fired at muzzle flashes whose source they could not see; whole lines loosed volleys into their own comrades by mistake; and when the brush caught fire, the wounded who could not crawl burned where they had fallen. The blind timber did not just confuse the battle. It claimed men a clear field would have spared. Roughly ten Confederate generals were killed or wounded in it.

Among them, Maj. Gen. John Bell Hood (South), leading part of Longstreet’s breakthrough, was hit by a Minié ball (the cone-shaped rifle bullet of the war) that shattered his right leg, and it was amputated on the field. Hood had already lost the use of his left arm at Gettysburg ten weeks before; Chickamauga took the leg. Brig. Gen. William H. Lytle (North), a Union general who was also a published poet, was killed leading his brigade. Confederate generals James Deshler and Preston Smith were killed as well.

And then there was Brig. Gen. Ben Hardin Helm (South). Helm was thirty-two, a West Point graduate Lincoln had personally offered a Union staff job at the war’s outset, and who had turned it down to go with the South. He had married Emilie Todd, a younger half-sister of Mary Todd Lincoln, which made him the President’s brother-in-law. He was mortally wounded leading his Kentucky brigade at Chickamauga and died the next morning. When the news reached Washington, it landed inside the First Family on the winning side of this Confederate victory. Lincoln grieved for him openly and privately, in a way that unsettled those around him; one senator who saw the President afterward said he had never seen Mr. Lincoln more moved. The same war the Union was fighting to end slavery had just killed the President’s own kin, in Confederate gray, in a Confederate win. The war had no edges; it ran straight through the house of the man directing it.

Bragg had won the bloodiest day of the western war, and threw the victory away. He did not pursue the broken Army of the Cumberland as it streamed off the field; he did not try to destroy it before it reached the safety of Chattanooga. The pressure to chase was loud and named: Lt. Gen. James Longstreet (South) urged a hard pursuit, and the cavalryman Maj. Gen. Nathan Bedford Forrest (South), riding on the heels of the fleeing Federals, pressed Bragg furiously to finish them. "What does he fight battles for?" Forrest was said to have raged when the order never came. Bragg, fixed on his own staggering losses, let the Union army slip into Chattanooga and then sat down to besiege it instead.

And then, in the weeks after, his army devoured itself from the inside. Bragg turned on the subordinates he blamed for the slow attack and the lost chance: he suspended and pressed charges against Polk, relieved D. H. Hill of his command, and watched his generals send a near-mutinous petition to Richmond begging for his removal. To break up the revolt, the army’s most powerful reinforcement, Longstreet’s corps, the very troops who had cracked the Union line, was detached and sent off to besiege Knoxville. So the army that had just won the field walked into the next round leaderless at the top, hollowed in the middle, and missing its hardest-hitting wing.

"It seems to me that the élan of the Southern Soldier was never seen after Chickamauga."

Maj. Gen. D. H. Hill (South), on the cost of the win. Élan, the dash and spirit, spent for the slaveholders’ cause and never the same afterward.

The siege of Chattanooga was where the South’s tactical triumph quietly turned into a strategic catastrophe. The trapped Union army nearly starved, men and draft animals dying of hunger inside the lines, until the crisis was broken in late October by a new supply route into the city, the "Cracker Line" opened via Brown’s Ferry on October 27. And the crisis brought the one man who would make Chickamauga not matter. Lincoln consolidated the western armies under Maj. Gen. Ulysses S. Grant; Rosecrans was relieved of command, and Thomas, the Rock, took over the Army of the Cumberland. In late November, Grant broke the siege at the Battles for Chattanooga, storming Lookout Mountain on November 24 and then watching his men make a spontaneous, unordered charge straight up Missionary Ridge on November 25 that broke Bragg’s army and sent it reeling back into Georgia.

So within two months, Chickamauga inverted itself. The South won the field, lost more men than the army it beat, failed to finish it, tore its own command apart in the aftermath, and handed the Union, two months later, the very gateway it had been fighting over.

The South won the bloodiest day of the western war and squandered it, refusing the pursuit Forrest and Longstreet demanded, then dismantling its own command in the recriminations that followed. Thomas’s stand saved the Union army, the siege that followed brought Grant, and Grant turned the defeat into the breakthrough that cracked the Deep South open. The only major Confederate victory in the West was also one of the costliest mistakes it ever made.