Why were Shelby and Rankin counties so Republican before the rest of AL & MS?

[jimrtex]

County boundaries can act as  filters.

Shelby County is on the interstate coming south out of Birmingham. It is outside the valley, and receives less pollution from the steel mills. It represents a fresh start. People before WWII didn't have much money, and this was even more true in The South. You get a white collar job and move to the city. But you have enough money for a car, and can afford a new house, likely quite modest, but better constructed. Wood rots. Wood in the South rots faster. A small cottage in Birmingham is expensive to maintain. You can't live in your parents house, because they're still living in it, its not in Birmingham, and there would be in-law friction.

You build new houses, and schools, and churches, and stores follow. Eventually doctors and dentists, and office parks. You don't have to be a Democrat to run for local office, since you don't have to advance out of the Democratic primary.

Rankin is similarly situated with respect to Jackson. It is across the Pearl River on the interstate traveling east. After an area has flooded several times, people get an idea not to rebuild there. There would be narrow bridges across the river, better than a ferry, but just. All of a sudden there are modern interstate bridges, and you can be home in Rankin County in 5 or 10 minutes.