In the late summer of 1862, the Confederacy tried something it had never tried before and would never manage again: it sent an army north to take a state away from the United States. The state was Kentucky, and the man sent to take it was General Braxton Bragg (South), commander of the Confederate Army of the Mississippi. His campaign has a grand name in the books, the Confederate Heartland Offensive, but the goal underneath the name was blunt and specific. Kentucky was a slave state that had stayed loyal to the Union, and Bragg meant to flip it: to recruit twenty-five or thirty thousand Kentuckians into the Confederate ranks and to install a Confederate state government in place of the loyal one in Frankfort, the capital. A Confederate Kentucky would be a slave state pried out of the Union and bolted onto the South.

Bragg was not doing this alone. A second Confederate army, under Major General Edmund Kirby Smith (South), had crossed into Kentucky from the east weeks earlier and won a sharp victory at Richmond, Kentucky. Two gray columns were loose in the state at once, Bragg’s from the south and Kirby Smith’s from the east, and the plan was for them to join, recruit a Kentucky army, and hold the state. The two-army shape of the invasion matters, because it is part of what would leave Bragg fighting his big battle with only a sliver of his strength.

The stakes had sharpened just weeks earlier, and not in the South’s favor. On September 22, 1862, President Abraham Lincoln had announced the preliminary Emancipation Proclamation, public notice that he intended to free the people enslaved in the rebelling states. The war’s purpose was visibly turning toward ending slavery, in plain view, at the very moment Bragg was marching to add a slave state to the Confederacy. That is the collision underneath the whole campaign: one army moving to widen slavery’s reach, a federal government openly moving to end it.

The political climax came four days before any serious fighting. On October 4, 1862, with Bragg’s army standing guard, the Confederates staged the inauguration of Richard Hawes (South) as the Confederate “governor” of Kentucky at the capitol in Frankfort, the only time in the war that Confederate forces seated a government inside a loyal state’s capital. Hawes told the crowd, in substance, that the old Union could no longer be put back together. He did not get to finish the celebration. Union artillery opened on the town in the middle of the ceremony, and the Confederates cleared out of Frankfort before the inaugural ball. The “government” of Confederate Kentucky lasted about an afternoon. To make it real, Bragg’s army would have to win the state on a battlefield.

Hawes’s line, that “the late Union cannot be restored,” survives only in later accounts; treat it as the gist of what he said, not a verified transcript.

But the deeper problem was that the people Bragg had come to liberate weren’t coming. He had been promised that Kentucky would rise for the Confederacy to a man, and he believed it: rolling along in his supply train were some twenty thousand spare rifles, hauled hundreds of miles to arm the recruits who were supposed to flock in. Hardly any did. In seven weeks in the state Bragg gathered only about two thousand Kentuckians, and, he complained bitterly afterward, half of those had already deserted. The rifles stayed in the wagons. The slave state Bragg had marched in to flip declined, by its own white population, to be flipped. That silence from the countryside was the first sign that the whole gamble was built on a fantasy.

It would do its fighting thirsty. A severe drought had been baking central Kentucky since around June. Streams that should have been running shrank to stagnant puddles, and across the region men and horses and wagons all groped toward the same shrinking water. Two armies were maneuvering through the same parched country toward the same few pools, and that, more than any plan on either side, is what set up the collision near a town of about three hundred people called Perryville.