The Democrat-Republican party was agrarian and anti federal. After the federal party collapsed there was a split with the agrarian Democrats and the more federalist types joining the whigs which became the Republicans. Democrats stayed largely agrarian/extractive until Roosevelt and particularly Truman realigned them to support more metropol interests. The republicans meanwhile largely supported centralized authority which has always favored the metropol until that switch. Now there's no Rockefeller Republicans left. That's why the American midwest is Republican. The southern strategy and race is a very important key, but land density usage is something you will see is not American specific in how these power coalitions form.