Was there any form of government that was stable (in terms of separatist revolts and cultural disputes) enough to maintain a fair lifespan, even though it had a diverse population [see footnote 1]?
How long did their lifespan last?
What made them stable?
How was the majority-minority (if they had any) relations?
What was the reason of their downfall?
[Footnote 1] A population that can be either composed of many different populations (varying by religion or just cultures), of just a big majority and a relatively small minority