So what caused the US political map to flip-flop in a mere eight years? What happened to cause the Southern states, proudly Blue and Democrat since the Civil War, to flip to Republican Red?

Why are the Red States Red?

What happened between 1956 and 1964?

Answer: The American Civil Rights Movement.

Actually, income growth and increases in wealth happened:

The Myth of the Southern Strategy

Is There Still a South? And Does it Matter?

This is also discussed in Earl and Merle Black’s The Rise of Southern Republicans.

Race was/is an issue in the South - there’s no denying that - but increases in wealth had more to do with the switch from the Democratic Party to the GOP than the Civil Rights Movement, and that can be backed up with demographic data as opposed to a couple of Presidential election maps. The move was gradual and we can look at the Congressional Districts and states which began moving into the Republican column and see that these are states/districts that were becoming wealthier. Also, the movement was not complete until nearly a generation after the Civil Rights Act was passed.

(Source: azspot, via think4yourself)