What is the political geography of the South?

[Del Tachi]

Like most of the country, Democratic strength is concentrated in big cities and majority-minority areas.  The South has a lot of rural, majority-Black areas (MS Delta, Black Belt, etc.) that are very visible on election maps but are generally way less populated than Republican-voting suburban or rural areas.  So while a state like Alabama may have a lot of Atlas-red counties, Democrats consistently struggle to break 40% of the vote.

Republicans dominate with White voters in the South, especially in conservative Evangelical areas.  Like other parts of the country, the recent trend has been for Republicans to do better with working class White voters than college-educated voters.  A lot of Southern Republicans are significantly more moderate on economic issues than social issues, with government support of some welfare and agriculture programs being broadly popular. 

Historically, most of the South was monolithically Democratic with a few notable exceptions (East TN, Texas Hill Country, etc.)  This began to change in the 1940s and 1950s as Southern agriculture mechanized and urban professions in cities and suburbs became more prevalent.  Urban and suburban Whites shifted to the Republican Party before rural White voters in the 1970s and 1980s, while today many of those same areas that first flipped Republican in the 20th century are trending towards Democrats.

This is generally the pattern throughout the South. 

[Del Tachi]

It's also worth noting that the initial shifts toward the GOP in some Southern states toward the latter parts of the 20th century weren't even necessarily fueled by native Southerners. For example, Georgia's political geography and statewide margins would have probably looked more like North Carolina's from 2000 to present if you negated the carpetbagger growth between 1975-1995 or so.

IIRC - Bush family has roots in Connecticut. And Bush Sr. was one of the "trailblazers" of Texas Republican party. So - this wasn't limited to Georgia. Nevertheless - local conservative Democrats (Gardner and Helms in North Carolina, Thurmond and Watson - in South Carolina, considerable part of "Byrd's machine" in Virginia, and so on) also played an extremely important role too..

Yes, the states that actually grew at relatively fast clips and had sizable economies (GA, TX, FL - maybe it could be argued VA and possibly even NC to some degree) were all affected to varying degrees by the broader in-migration. It's not as if the trends that began to spill over into rural areas wouldn't have happened regardless, but the statewide effects at minimum would have been delayed and - in states like GA - possibly could have led to the state never leaving swing state status (at least for non-federal elections) if everything else (i.e. Obama coalition etc) played out the same. Pretty much like how NC has been with its Democratic Governors and statewide officers.

Looking at old maps and list of congressmen, to my uneducated eye it looks like the South would've had three parties in a parliamentary system;

1) A suburban movement conservative party (aka the GOP)
2) A centrist (at least economically) rural southern white party
3) An urban/black belt liberal party

Yet the latter two were confined within the Democrats. How did that work within the Democratic Party and the Southern legislatures between the VRA passing and the transition of rural Southern whites to the GOP?

Groups 1 and 3 were never really severely challenged Group 2's majority (in state legislatures, at least) until the 1990s and 2000s.  There as long been an unspoken alliance between Groups 1 and 3 to create as many VRA districts as possible, thus expediting the decline of Group 2. 

Nevertheless, there were some brief moments when Groups 2 and 3 held together a shaky electoral majority, and were able to elect progressive Democratic governors like Cliff Finch (MS, 1976-80), Jim Hunt (NC, 1977-85 and 1993-01) and Jimmy Carter (GA, 1971-75).

[Del Tachi]

I wonder how much of a role the GOP abandoning protectionism after Smoot-Hawley played in breaking the Solid South. The Solid South hated tariffs as much as anything else.

As unionized elements within the Democratic Party came to prominence during the 20th Century and pushed for increased protectionism, this certainly helped to push the South away.  However, I would argue that "tariffs" were pretty much done as a partisan issue in the U.S. by the end of World War II or so.