Vitriol and unrest

If the United States was divided in sectarian lines - say the middle and South of the country were populated by followers of fundamentalist sects, while the costal regions were mostly inhabited by adepts of mainstream Christianity, with significant Jewish, nonbeliever, and other minorities - then a Syrian-style civil war would be a distinct possibility.

All that would be needed is a tremendous amount of hatred such as that seen in right-wing blogs, and an unstable, corrupt, and authoritarian leader.