A century plus earlier, this was the same region trying to secede from the country and, now I'd argue, it's one of the most patriotic regions of the USA.
If you accept the premise, how did this happen and what were the pivotal decades/ events that lead to it?
This is a very complicated question with a lot of facets that i'll bring up. The main ideas being the south is much more conservative than the rest of the country, the history of the confederacy still lingers, and their economy isn't as robust. Essentially the more isolated you are the more you'll favor what you know (this is in terms of physical separation like in lack of trade or ideological separation in being religiously dogmatic).
A great discussion on why the south is more religious can be found here.