Half of Germany was a communist country until 30 years ago while the other half was a wealthy democracy. Not sure how much more heterogenous than that you get, politics-wise. There remain fairly dramatic political differences between the former east and west.

My second hand understanding, though, is that west Germans consider East Germans to be the same people and the integration was viewed as a reunification. Not quite the same as different groups who perceive themselves as distinct and with conflicting interests.