Again, that's not necessarily the case. A domestic population can be displaced, but that doesn't necessitate the deterioration of a a domestic population's social cohesion. That's a failure of the domestic populations social institutions. This is why (actual) refugees from invading armies still have social cohesion. In fact, they may aggressively seek to preserve their social order, even when displaced to other lands by an invading force. This is why we see some populations "cling to religion" when they are displaced.

What you're thinking of is a) failed integration, and b) social institutional failure.