Colin Woodard wrote American Nations: A History of the Eleven Rival Regional Cultures of North America, which suggests some reasons for the Deep South's cultural development to date. But I don't know how well it was received by academic historians. As for post-Civil War politics, I can speak directly to that subject. Southern whites were markedly more sympathetic to the Democratic Party during and after the war. After Reconstruction, Southern whites enacted laws and practices to keep African-Americans from voting. Democrats maintained something like a one-party system in the South through the 1960s, with factional politics "filling in" for the "missing" Republican Party (see V.O. Key and those who've debated his "Black belt" thesis about Southern Politics). In the 1960s, however, Northern Democrats won enough influence in the party to push forward an ambitious civil rights agenda. When combined with Richard Nixon's 1968 "Southern Strategy," this shifted the loyalty of white Southerners toward the Republican Party over time, a process that was more or less complete by 1980 and which continues to this day.