I still think religion is the poison planted long ago and soaked up by the roots American culture which continues to make it difficult to impossible to awaken people to the many cold hard truths of life, without offending their sense of community and traditional values. Religion does a lot of damage to people's ability to think introspectively. The rest is just a clustering phenomenon, where you have a schism between the people who finally "got it", left the country, and relocated to more industrialized areas, and... everybody else. Convince those remaining rural residents that the city slickers are "elitists", etc., and you have a winning strategy for highly successful divisive politics.