One idea of a nation is it's like a tribe, a large group with some shared ethnicity i.e. common customs and language. "These are my people" say the denizens of such a nation.
Another idea of a nation is a kind of cybernetic machine that lets people of many ethnicities co-exist. This is not a recent idea or invention. The value "cosmopolitan" comes to mind, as older than "multicultural".
The federations of states in North America, including those of Lower48, along with the provinces of Canada, have internalized a lot of the "melting pot" aesthetics that go with the cosmopolitan mindset, although acceptance of diversity also allows for niches and enclaves (or call them "ghettos" as in the "Buddhist ghetto" like where I live -- also known as Asylum District), so-called neighborhoods.
That my family should have to live next door to some other family of greatly different heritage seems unfair and wrong according to the first set of criteria. The Clint Eastwood film here is Gran Torino. The retired factory worker from Detroit resents having to live next to refugees from Asia -- until he gets to know them better.
People in the federated states of North America tend to see a state as cosmopolitan and cybernetic, unless they feel threatened by such notions, in which case the idea of fragmenting into local "stans" may be attractive. Some people suggest that, if you want a "whites only" experience (as if "white" were either a race and/or ethnicity, whereas it's neither), you might try moving to Idaho.
To cosmopolitan ears, the parochialism of "Ukraine for Ukrainians" meaning "Russians go home" sounds like nationalism of the first sort. More like Kurdistan, a place for Kurds. On the other hand, many European nations, especially those with a colonial past, have embraced the values of cosmopolitanism. Their idea of a state is it should work for multiple ethnicities.
India supposedly wants to stay multicultural, meaning Hindu and Islamic subcultures get to share the same infrastructure. Again, the temptation is to give in to tribalism, more like some Ukrainians, some Americans. States that know how to accommodate multiple ethnicities might be more experimental, but then in principle they may be more robust, as they better mirror the whole earth in microcosm.
We might ask similar questions about corporations, sports teams, religious institutions: are they able to hold it together even when there's lots of diversity? That's a question to ask more than to answer. The jury is still out in so many cases, meaning Judgement Day has not yet arrived, apparently.
What hurts Ukraine's prospects of staying in the game, as a nation, are its ultra-nationalists, the ones who say "Ukraine is for ethnic Ukrainians only". That's an attitude Europeans are taught is immature, too immature to be a basis for statehood. Ukraine's inability to stomach its own Russian population seems to have doomed it from the beginning, at least in the eyes of some spectators.
Ethnic chauvinism may be safely repackaged as "pride" around which parades are permissible, even festivals. But raining on others' parades is considered gauche and rather tasteless, as a rule of thumb. Again, I'm speaking from a globalist perspective. Tribalists will take a different view.
When it comes to tribalism, that's where I believe in "diaspora nations" and/or "virtual nations" that don't need to claim vast tracts of contiguous land. Ethnicities cohere more through telecommunications than through sharing common acreage. We could call a supranational corporation, say Global Data Corp, such a tribal ethnicity, although again, management may value diversity along several axes, without surrendering the company's tribal nature.
