Actually as an ethnic chinese with family still in mainland (even in the "Party"), this makes absolute sense, China will always argue for territorial integrity, especially since it contains massive minority within its fringe regions that they consider as part of their indivisible "core". So in international relations they would also argue for territorial integrity for nations with massive minority population on their fringe regions.
It's a bit more nuanced in the Balkans and Ukraine, although I totally get the 'old state' policy of claiming it's 'their' land, and unfortunately Ukraine does it too. Most of the time those people just want more freedom in their regional choices, regardless of who 'the state' is. And, if it gets so bad that they want a state of their own or 'the state' doesn't allow them to exist, the question that arises is why is that the state's land. I should know, I come from a country where the state basically plugged its ears and pretended a minority doesn't exist. (actually, it's more like two or several, but the second one is universally hated so nobody cares, and the others are usually too few to get noticed).
Ukraine has regions where literally ethnic russians are the majority and the Ukrainians are the 'massive minority', yet that is Ukrainian land. It goes deeper, most of the russians there were brought half a century ago under Stalin, to 'colonize' and replace the ethnic ukrainians who teleported to the arctic. That also brings the question of what 'defines' a country. Its land? Its people? Infrastructure? A mix of all of the above? One could say that ideally this could have been defused partly even by giving greater autonomy and acceptance. Partly as in Putin might have invaded anyway because in all his 'reign' there's an acute lack of diplomacy and several cases of using wars and bloodshed to 'solve' popularity issues. And that's also something you see in the Balkans. Big state goes to war against small neighbouring state because they're easy and 'different', so it makes portraying them as enemy. I might be wrong, I haven't really looked into it that much, but most of the Yugoslav war can be summed up as 'christian old-school Serbia going to town on their muslim neighbouring country'. And that might have even been due to generals and leaders with grandiose dreams that found themselves irrelevant in the 90's and felt the need to kick stuff up.
Edit: Not to say that the russians there are 'guilty' of being in Ukraine. That in itself is no fault of their own, as the 'beauty' of dictatorships is that the average Joe doesn't get to have a say. And then some of the younger ones were born and lived in Ukraine all their life. For all intents and purposes, they're locals. Now, they can either try with autonomy (good luck with that in the current situation), but the opposite would basically mean telling them to f**k off to Russia cuz they're on Ukrainian soil (and, believe me, land claims and properties of the 'dislocated' are still very much a thing in former USSR countries, even now, so there may be Ukrainians eager to reposses grandpa's land that he had before he took the train to the Urals).But that , in itself, would still amount to 'deporting' the locals, so in a way, they'd be no better than Stalin.