Earlier quoted context omitted.
Turns out that when you have 330M people with completely incompatible ethnocultural backgrounds, you end up with an untenably wide variance in political beliefs. Europeans take note; this is where many of you are heading.
Wouldn't your thesis predict more political problems in areas of greatest diversity (ie, cities)? The cleft in the US runs mainly between rural and urban populations; ie, between high-diversity and low diversity areas. Each 'system' seems to find political equilibria just fine on their own. (Or, in a more flippant form: I hadn't noticed Toronto had become a hellscape of inter-ethnic conflict...)
No, it would predict political division along racial lines, which is precisely what happens.
> The cleft in the US runs mainly between rural and urban populations
This is a weaker predictor than the racial demographics of the voters.
> high-diversity and low diversity areas
Are you using "diversity" as a synonym for "nonwhiteness"? Because if so, you're correct, but you could probably phrase this more explicitly.
> I hadn't noticed Toronto had become a hellscape of inter-ethnic conflict
Political rifts, which is what we are talking about, don't (usually, yet) manifest as visible ethnic conflict in the US either.