We have allowed this post because it is a valid question, but please remember that you have been warned strongly in the past for soapboxing on this topic. If you mainly view this thread as a chance to argue, we will warn you even more strongly.

Well, first it's important to note that politics aren't always driven by clear ideological divisions. The political parties of the gilded age were not ideologically cohesive, but rather different blocs held together in tactical alliances. There were certain issues these blocs might agree on, like tariffs, but it was also largely just driven by the pursuit of power as a means to patronage. This is how you got very strange bedfellows like the Democrats being the party of both immigrant Catholics and Southern Democrats who were aggressively anti-Catholic and the Republicans were host to both urban reformers and corrupt industrialists.

Second, it's important to note that the particular issues that are relevant, and the nature of those issues, will shift from one era to the next. The South used to be a hotbed of economic populism in the early 20th century. However, economic populism of the era was largely agricultural in character, so when the economic issues shifted to those of a more industrial and post-industrial economy the South wasn't necessarily going to follow.

As for the civil rights driven shift in party allegiance associated with the southern strategy, that was a gradual and ad hoc process. Essentially, in the early 1900s Southerns were almost uniformly Democrats while black voters would more likely be Republican (though this wasn't particularly strong). However, in the 1930s black voters shifted towards the Democrats, essentially recognizing the benefits of New Deal policies. Moreover, northern progressives/liberals had been gradually shifting to the Democrats in the first few decades of the 20th century as the Republican party decisively became the party of industrial capitalists, and by the end of WWII these voters were generally in favor of racial equality. By the 1950s the Democrats had a sizeable base that was for Civil Rights that was larger and more strategically valuable than the Southern Democrats who opposed it, and so they catered to them. Republicans caught onto this, and so they gradually coopted Southern democrats. This is often seen as a dramatic shift, but institutional inertia, partisan loyalty for its own sake and the fact that politics is driven by far more than just civil rights issues meant the process took decades to fully realize. For example, while Southern Democrats were increasingly hostile to the party's racial platform, their status in the party meant they still got a lot of senior chairmanships in Congress, so they weren't eager to change parties. It wasn't until the Republican Revolution of 1994 that the bulk of the old Southern Democrats had either switched sides or died out.