As is so often the case, the answer simply lies in decentralization.
If not being culturally united is the "problem" is that really the "answer"?
“If not being culturally united is the “problem” is that really the “answer”?”
It could be a temporary or even a permanent answer. Look how long Switzerland has lasted, a tiny country with 4 different languages and subcultures. Most of the political power there rests with the cantons, not the federal government.
Thing is if an arrangement among various groups is not working out than disband it and let each group do their own thing.