Next to a nuclear strike, foreign invasion, or global pandemic, it’s hard to imagine something as bone-chillingly terrifying as a second hot Civil War. The first one was bad enough, what with the endless carnage and the deaths of over 620,000 soldiers in a time when the U.S. was sparsely populated and wartime technology was in its relative infancy, at least compared to today. Even if the military withheld its most destructive weapons, a modern hot civil war would be disastrous on a scale that’s barely imaginable. It’s a prospect no sane person wants, even on the fringes of the...