I've searched but couldn't find anything up on it. In a very general sense, and I'm looking mostly at Europe/North Africa/Western Asia- with any PoD post-1000ish is it possible to reduce the balkanization of states by nationality or language? This is a really, really broad question and it's open to any time post-PoD (1200s, 1800s). By fractioning I guess I mean "balkanization", I explain a bit more below.
What I'm thinking of mostly is in multi-ethnic regions like the Balkans (particularly in the Carpathian Basin and the Ottoman Empire), or the border regions alongside the Germanic regions of Europe and Slavic Europe, France pre-revolution (with many spoken variants of Langue d'ocs and langue d'oils), etc. Was it inevitable that many of these cultures and regions would push for independence and autonomy, or would it be possible to have more multi-ethnic oriented nationalities develop in some places. I'm really phrasing this poorly I know but hopefully you sort of intuitively get the question. I'm not looking to prolong these empires or states specifically: I'm speaking in very general terms. Multi-ethnic empires seemed sort of like the norm in many places pre-Industrial Revolution/French Revolution, and then after that for a plethora of reasons (some which could be expounded on by any knowledgeable persons here) it seems like nationalistic consciousness developed in many places.
But it doesn't seem like it has to be that way everywhere. China for instance, while having many unique and un-European problems associated with its unity, manages to maintain a "Chinese" identity despite quite large differences in language, generalized appearances, geography, what have you. Would there be any way for large empires in Europe (or Central Asia being another interest) to maintain many more different languages and dialects, cultures, etc. than OTL while still forging a national identity similar to one being Chinese? *EDIT:
Another state that comes to mind is Switzerland. This is more as to what I'm getting at. How would it be possible to encourage more development of "Swiss" like states in Europe; where multiple ethnicities and languages are included? Not asking for everyone to be friends, Europe a happy patchwork of friendly neighbours, etc. Just wondering if more diversity and less singular language tunnel-vision when it came to state-building was an inevitable casualty of nationalism, or whether it was realistically plausible to see more Swiss-like states emerge in Europe (as many parts of Europe are not geographically contingent when it comes to ethnicity).
Sorry for the messy question as well, I had a lot of trouble thinking it out. Thanks for soldiering through it

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