The Kentucky campaign was already three months old and no decisive battle between Bragg and Buell had yet taken place. The Confederates had achieved many of their goals. They had positioned large, powerful forces in the heartland of the state, gathered enormous amounts of supplies, and taken the strategic initiative away from their opponents. But they had not been able to consolidate their hold on the state, and their position had become precarious. Buell now had an excellent opportunity to kick the Confederates out of Kentucky.
The Army of the Ohio began to enter Louisville on September 24 and continued to march into the city for five days. As soon as his headquarters reached Louisville, Buell began to prepare for an offensive against Bragg and Smith. He had no time to waste. The country was excited about the Confederate invasion, and Buell was under great pressure to take action immediately. To his credit, he accomplished a great deal in a short time. He thoroughly reorganized his army while at the same time incorporating many new units into it. Buell had received three divisions from Grant's army in northern Mississippi and western Tennessee and took in all the units of Nelson's Army of Kentucky. He divided the enlarged force into three new corps. McCook commanded the I Corps of thirteen thousand men, Crittenden led the II Corps with twenty-two thousand men, and Nelson commanded the III Corps of twenty-two thousand troops. Each corps had three divisions. Thomas, Buell's best subordinate, was named second in command of the army. With fifty-seven thousand men, Buell greatly outnumbered Bragg's and Smith's armies. Only by combining in a timely manner and acting under a single commander could the Confederates hope to have a chance of staying in Kentucky.