Okay here's Brad's take. Following the Civil War, i.e. reconstruction, the south was all totally controlled by the democrats. After all Lincoln was a republican. The republicans stood for strong federalism at that time, and the democrats stood for states rights. It was just a political continuation of the war. Over the next 100 years the democrats of the south built, grew, and perfected institutional racism, which has at its core the Jim Crow laws. Blacks couldn't legally get loans, buy good land, go to good schools, restaurants, etc. They could hardly even leave black town except to go into white town and work for slave wages. Black town mostly wasn't provided with things like sewer service or electricity even though they were taxed.
When elections were near, a random black was hanged in damn near every county as a warning not to go to the polls to vote. All of this was orchestrated by the southern democrats otherwise known as dixiecrats. This caused a lot of political tension with the south's traditional enemy, New England.
Along comes LBJ, a southerner. He joined hands with the New Englanders to pass the Civil Rights Act, saying something like "I believe we (democrats) have just lost the south for a generation" or words to that effect. He was right. It left the dixiecrats of the south without a political party affiliation. So Nixon developed "The Southern Strategy" which was for the republican party to court the southern vote with "dog whistle" phrases indicating sympathy with the racist cause. The phrase "states rights" came to mean support for the Jim Crow laws. The dixiecrats joined the republican party en masse in 1968. Reagan followed up the southern strategy by promoting anti-federalism. Our two major political parties had officially switched roles.
Looking deeper, what we are seeing is the echo of the Great Awakening of the 1830's which saw disenfranchised anti-enlightenment religious zealots fleeing London for South Carolina. Their charismatic cults grew and spread across the south by promoting "gospel prosperity" which refers to the fact that the sudden economic growth from free land (taken from Indians) and free labor (from Africa) were mistaken for god's special favor. From 1830 until 1865 the Southern Methodist newspaper grew into the largest circulation of any paper in the world. Every issue (still libraried and available) had front page articles quoting the Bible in support of slavery. The Southern Baptist's newspaper did the same. During that same time period the Methodists of New England split off and formed their own conference, and re-printed the Bible replacing the word "slave" with "servant" where ever it occurs, which creates some rather awkward sentences.
Like any historical story, you can always take another step backward to see how the previous generation set it up. The religious wars of Europe begat the Great Awakening. The Protestant Revolt gave rise to the religious wars, and so on.
People who don't see the connection between religion and politics understand neither. Anyway that's my take.