I will present you three maps.
1. Bible Belt of America

2. Confederate States of America

3. Red and Blue States for the last 4 elections

Did you notice the correlation? Bible Belt = Confederate States = Republican. Is it just a coincidence or is there a reason for this? As it turns out, there is a reason for this.

1864 Elections where Abraham Lincoln won. The same North-South divide exists. But, he is a Republican.

1868 - Despondency in South and Republicans won. But an anti-Republican front is forming for what happened in the Civil War.

1876 - The fortress is complete.

The game went on till...1960. What changed? Civil Rights Movement. Democrat Presidents JFK and Johnson passed laws to make Blacks equal to others in American society. South Flipped against Democrats again.

Except in rare cases, the fortress stood. Inferences?
1. The Civil War of 1865 launched against removing slavery. They lost the war and showed their anger against the party Lincoln represented.

2. The Civil Rights Movement which gave equal rights to Blacks angered the same people again. What do they do? They do exactly what they did after the Civil War - make the party which did that non-existent.
A military civil war is not an option anymore and

they do the next best thing - punish electorally to the stage that the party which did that becomes a joke in elections. Florida is slightly different because of it's tourist income and Cuban refugee flood. Except that states, rest all showed a near complete consistency.

A small slip. 1864 - Confederate states, no elections were held. The division existed in 1860 as well. Lincoln for No Slaves and South for Slaves.
https://twitter.com/cbkwgl/status/1347472855395536898