The Battle of Perryville was caused by a Southern invasion of the state of Kentucky. This state, though in the South, had remained a part of the union.
General Braxton Bragg was the commander of the CSA's Army of Mississippi. He had managed to lead his army through Tennessee and now was going to attempt an invasion of Kentucky. The idea was to conquer that state and bring it into the Confederacy. This would gain new recruits for the CSA, give it a new source of supplies, and force the Union to divert troops to the state to fight. As the Confederate forces moved through Kentucky, Union forces moved to oppose them and prevent them from taking important cities such as Louisville. The two sides' movements brought them to Perryville where the battle took place.