1980:
1984:
1988:
1992 and 1996 were a schism because of H Ross Perot, but they show mostly the same overlap with previous maps. The great lakes areas and New York/New England vote as a block, and the West coast votes as a block. 2000:
2004:
2008:
2012:
Now if you are talking before 1980, this is true, because the southern states were democrat, and it took Reagan to flip them to Republican. Socially though, all the red states in the preceding maps represent an affinity for each other in terms of culture and income. They have a lot in common with each other, and the maps I post are meant to represent what would have happened to the Confederacy had it continued in absence of a war.
Those states would have flipped, and it would have left the Great Lakes/New York self interest zone which still controls our politics today.
In your own biased view westerners and midwesterners wouldn’t want African-Americans around any more than they wanted competition from slaves or haughty slaveowners so they’d tell the CSA to P.O. and FOAD.
There would have been no great migration of slaves into the western territories. Those areas cannot support large scale slave farming, and slaves were too valuable in the cotton growing regions to waste on the western territories.
As i've pointed out, there were only a dozen slaves in the entire New Mexico territory by the 1850s, and at that time no one was putting up any opposition to it.