The south voted almost unanimously for FDR 2 times, and FDR 4 times. Only recently has it switched places with New England.
For all his faults, FDR’s administration was the first one that put more federal money into the South than extracting money out of the South. The legacy of the war, the Occupation and the ruinous Morrill Tariff had in the words of one administration official, reduced the Southern states to the status of “a colony”. This had been the richest region of the country until the war.