The southern states were a large democratic voting block for much of the history of the democratic party, particularly after the civil war. If I recall correctly the Democrats' mascot of a donkey was created in reference to the Southern Democrats' dogged stubbornness to change or entertain other political options. A popular term for southern democrats is "dixiecrats". Several democratic presidents (Wilson and Johnson come to mind) were themselves dixiecrats. Moreover the relatively instantaneous shift of southern voters from Democrat to Republican is perhaps one of the most bizarre and fascinating topics of american political history of the last 50 years.
But I mean I'm not really very up on US history, this is just what I vaguely remember from my High School history classes. I could be totally wrong.