We've been through a Great Depression before. Economic and social lines were at least as strong then as they are now. At least we don't have Jim Crow laws now. Now, we have two coasts that are considered urban, not one, so it's actually somewhat less of an urban vs. rural divide (remember that whole Manifest Destiny thing?).

As a nation, the U.S. is more uniform than it is then so any such theory would have to explain how this is to our detriment, how an increase in similarity can actually provoke serious infighting, because the psychology research shows that people who are more similar tend to get along together in the long run. More than that, we just elected a uniter, who seems to pick good advisors no less.

So in all, I really want to see this classified information, because we've been through pretty bad times before (that's pretty good evidence, yes?) and this country didn't break up then.