[Travis McGee]

I disagree with your #1. Plenty of Civil Wars erupt where there is even less geographical stratification, or a similar amount. Spain 1930s, Argentina 1970s, El Salvador 1980s, Bosnia 1990s etc. If anything, Civil Wars within such blended and marbled societies are even more vicious, as a first step is "ethnic cleansing" of "enemy" enclaves.

[headsonpikes]

I believe that the 'Social Wars' of Late Republican Rome provide a gut-tightening parallel to America's situation.

Within 50 years of the end of those bloody conflicts, after a period of dictatorship and other extra-Constitutional adventures, the Romans lost their centuries-old Republic and dwelt under a divine Emperor.

Faction is the deadly enemy of Republics.