I read mostly history and it was my college major, so I appreciate your interest. Since we only have two major parties in the U.S., it helps to view each one as made up of diverse parties-plural, with roiling regional and cultural factions within. Therefore, to understand the parties, it helps to understand the nation’s regions. The best book I’ve read in a long time is American Nations: A History of Eleven Rival Regional Cultures of North America by journalist Collin Woodward. It will sharpen a reader’s understanding of our country’s otherwise seemingly unintelligible politics and, to some extent Canada and Mexico’s too.