True, as a species we all but glorify conflicts... but I think democracy does require some degree of social cohesion. I see a lot of danger if our continent-spanning superpower starts to crumble due to internal divisions, especially considering we don't have a clear path to secession.
I wouldn't bet on the US's longevity. Read Peter Turchin, War and Peace and War (discussed here a week or two ago), particularly noting his part about how multiple imperial peoples can't coexist in a single country...
The Fourth Turning -- on the patterns that generations tend to fall into -- might also be interesting.
