As an American, you just gave a better context for the stuff I did understand than most Americans could.

The colors weren't red and blue back then, they were Navy Blue (North) and Grey (South). While it's true that most of the south was predominantly Democrat back then, the events leading up to and including the Southern Strategy in the mid to late 20th century, cause the Republicans to stop being the progressive party, and become the fascist party. The Democrat didn't really move much to the left during that whole mess. That is why you'll see the southern states being referred to as red states today, because they are gerrymandered to guarantee Republican victories.