The new Economist survey of America looks at the current state of what Americans always had in common and what made US society successful in the past, namely mobility, immigration, equality of opportunity, and civic associations:

Voluntary associations are reviving, though only after a long period of decline. But disturbingly, there are signs that social mobility is dwindling. The political system, for its part, is adding to social rigidities instead of counteracting them. The problem is not that America has become less dynamic. Its society continues to grow and change as fast as ever. But traditionally the country has been seen as a melting pot, which after much stirring produces greater integration. Now some of that activity may be causing separation.

The Economist concludes, however, that

America, with its extraordinary resilience and dynamism, has survived plenty of conflict in the past. Indeed, its very dynamism creates both conflict and the strength needed to overcome it.