What broke at Chancellorsville, in the end, was not the Union army. It was Major General Joseph Hooker’s (North) will to use it. He still had tens of thousands of men who had barely fired a shot. He still outnumbered Lee. But after the porch and the concussion and the collapse of his line, the fight had gone out of the man at the top, and an army cannot be braver than the general commanding it.

Lee was now the one dividing his attention. With Hooker passive and pulled back into a tight defensive horseshoe near the river, Lee turned part of his army around, away from Hooker, to deal with Major General John Sedgwick’s (North) breakthrough in his rear. He was fighting in two directions at once and winning in both, against a combined force more than twice his size, because the larger force had stopped believing it could win. Major General Lafayette McLaws (South) and the returning Major General Jubal Early (South) hemmed Sedgwick in at Salem Church, and on the night of May 4 into the 5th Sedgwick gave it up and pulled his corps back north across the Rappahannock over pontoon bridges (temporary floating bridges thrown across the river) at Banks’ Ford.

That left only Hooker, dug in with his back to the river, and on the night of May 5 into May 6 he quit. With Sedgwick repulsed and his own nerve gone, Hooker recrossed the Rappahannock to the north bank and ended the campaign. He had brought roughly twice Lee’s numbers across the rivers and behind the Confederate army, and he carried them back across beaten by an enemy he had outnumbered the entire time. It is, fairly, called Lee’s masterpiece, his perfect battle, by the historians who have studied it. Outnumbered two to one, he had divided his army twice, out-thought and out-nerved a larger and better-positioned foe, and sent it packing.

But the word masterpiece hides the bill. The casualty lists tell a darker story underneath the brilliance.

The two armies between them lost somewhere around 30,000 men in roughly six days of fighting in tangled woods that hid the dead and trapped the wounded. The horror of that ground had its own signature: brush fires, set off by shellfire and musketry in the dry second-growth scrub, swept through the thickets, and wounded men of both sides who could not crawl clear were burned where they lay. In raw numbers the North lost more, around 17,300 to the South’s roughly 13,000. But measure each loss against the army it came out of, and the brilliance curdles: out of Hooker’s roughly 130,000, the North’s dead and wounded were about one in eight; out of Lee’s roughly 60,000, the South’s were better than one in five. Lee bled a far heavier share of a far smaller army. It was a victory his army could not really afford to keep winning.

One of the 13,000 was Jackson. He had been carried roughly twenty-seven miles south to an outbuilding on the Chandler plantation near Guinea Station to recover away from the front. There the wound did not kill him; pneumonia did. On May 10, 1863, eight days after his own men shot him in the dark, Stonewall Jackson died, thirty-nine years old. His reported last words were that they should cross over the river and rest under the shade of the trees.

That death reorganized both armies and the war. Lee, with no one who could fill Jackson’s shoes, broke his two corps into three and handed two of them to men who had never carried that weight, and at Gettysburg, eight weeks later, the new commanders would hesitate on the first evening exactly where Jackson would have pressed. On the other side, the defeat finished Hooker. Within weeks Lee was marching north into the free states, into the teeth of the new emancipation policy; Hooker quarreled with Washington over reinforcements, offered his resignation in a temper, and Lincoln took it. On June 28, 1863, three days before Gettysburg, Major General George G. Meade (North) was woken in the dark and told he now commanded the Army of the Potomac.

Confederate victory: Lee’s tactical masterpiece in the Wilderness, won by sheer audacity, and the most expensive win of his career. A fifth of his army was gone, Stonewall Jackson was dead, and the reorganized command would falter two months later at Gettysburg. The perfect battle was the launching pad for the campaign that broke the Confederacy in the East.