Enlistments at the North had so far fallen off that drafts must be made in order to maintain that great superiority of numbers without which the North, fighting aggressively, could not hope to make head against Southern defense, as all the operations of the war up to that time had shown, and as the later course of the contest additionally proved at every point.
But Bragg's effort to seize Louisville before Buell could throw himself into that city's defenses, failed of its purpose. By virtue of a wonderful march Buell reached the city first, near the end of September, the last of his forces arriving there on the twenty-ninth. Bragg was at Bardstown, not far away and in a very threatening position. In the meanwhile Grant held his own at Corinth in spite of the dangerous depletion of his forces, and the whole of West Tennessee remained in possession of the Federals.
Buell found heavy reinforcements awaiting him at Louisville, while Bragg at Bardstown had not yet been joined, as he had expected to be, by Kirby Smith's force from eastern Kentucky.
The conditions of the campaign were thus reversed. Buell, who had been on the defensive and in enforced retreat, was able now to take the offensive, while Bragg, who had been advancing with high hopes was now in a position from which he must retreat promptly on pain of having his army overwhelmed and destroyed.
Buell quickly reorganized his army into corps, welding the raw troops into the seasoned force, and within a day or two he was ready to assail the enemy who had driven him across two states.
Bragg retired to Perryville with a total force of about 35,000 men, and Buell with 58,000 advanced upon him. On the eighth of October a severe battle occurred which lasted from noonday to night and seemed undecided when night fell. But when morning came Bragg had retired and was in slow and orderly retreat southward. The Federal loss in the battle of Perryville was reported at 4,348, including two brigadier generals killed. The Confederate loss is unknown, but as Bragg began the battle with only three divisions assailing eight, and as the fighting at times was muzzle to muzzle, the slaughter among such troops as were actually engaged on his side, must have been terrible.
Learning that Kirby Smith's command had on that evening joined Bragg, General Buell did not press his enemy, but disposed his forces for a defensive battle. It was not until the thirteenth that he discovered that Bragg was indeed retreating and ordered a pursuit. This was pressed, with some fighting now and then, as far as Crab Orchard, where the Federals halted, leaving Bragg free to make his leisurely way to East Tennessee with an enormous wagon train loaded with a rich booty of supplies which he had gathered in Kentucky.