The majority of southerners are God fearing, gun toting, pro-life, and religious people. When the Democrat party became the big government, welfare party, the south changed to the GOP. It really took off with the election of Ronald Reagan.
When asked this question, liberals sneer in reply that racist white Southerners, the real Ku Kluxers, left the newly `progressive’ Democrat Party because they couldn’t stomach its sudden excessive solicitousness toward blacks, and turned instead toward the party of the `hellish Nixon’ which stood for war, reflexive anti-communism, and trusting narrow-minded white citizens with their guns.
However, the worst of the Southern racist politicians were Democrats, every last one. Not just Herman Talmadge and Pitchfork Ben Tillman, but the execrable Jimmah Carter who ran for governor in 1970 & defeated his opponent by depicting him as too liberal & pro-black for Georgia.
The Democrat party was McGovernized in 1972 and has been extremely liberal ever since. Without the slavish support of the black vote it would have become marginalized by now into the party of the coastal urban elites.