Thanks for the comprehensive reply. It made me think of something, of why the dems and republicans essentially swapped voter bases over time (or why this general dynamic in any given scenario would take place). In the beginning, Republicans had the black vote and the northern vote predominantly. Dems had a lock on the south. It's only natural to eventually want to expand your constituency and absorb those voters who traditionally haven't supported you. Thus, Dems finding ways to appeal more to blacks and northern whites, and Republicans finding ways to appeal more to southern whites. All while probably trying to retain their original voter base. And there you have a general framework of why, over time, 2 political parties can essentially swap places on the policies they support and the constituencies that support them.

I heard another theory that also seems to hold validity. A prior major shift was during the 1930's. Poor and working class folks (a lot of them African Americans) moved to the Democrat party during the New Deal policies which appealed to lower-income individuals.

When and why did African Americans make the switch from mostly voting Republican to mostly voting Democrat?