Why Polarization Recurs Across History

What do propaganda posters have in common across nation and time, and how is that related to the medial prefrontal cortex? What is behind repeating cycles of societal polarization? What does any of this have to do with the American Civil War, hippies vs soldiers, border ruffians vs free-staters, hanging chads, Pearl Harbor, and why education can serve as an immune response to mind viruses?