FYI - Quebec has had 2 referendums on separation. The most recent, 1995, the “No” (No to “a mandate to negotiate separation”) side won barely by about 1%. Later it came out that a little less than 2% of the ballots were rejected for being marked improperly - with allegations these were “no” votes rejected by the separtist governmnet workers running the referendum. After that the federal government inroduced the Clarity Act
the Liberal government passed the Clarity Act, which stated that any future referendum would have to be on a “clear question” and that it would have to represent a “clear majority” for the federal Parliament to recognize its validity. Section 1(4) of the Act stated that questions that provided for only a mandate for negotiation or envisioned other partnerships with Canada would be considered unclear, and thus not recognized.
Clear majority is not specified, but the general feeling was that the country should not split up based on a difference of a few percent, particulalry as polling sentiment shifts a few percent from day to day. (Brexit, anyone?) Clear question is also required. There was the usual politicl shenannigans - the federal debt at the time was $600B so some “yes” propagandists said that if separation happened, Canda would have to pay Quebec $150B as its share (people unclear on the concept spreading manure). The separatist elite in the Quebec government insisted as a distinct peoples, the French had the right to sovereignity. When presented the reciprocal agrument from the aboriginal population which was the dominant population in much of the North, they said “of course not…” (the goose-gander principle.) Similarly, whether Quebec would keep those aboriginal territories given to it by Ottawa well after it entered Confederation as a province, with their minerals and hydo-electric power, “mais oui!” they said. What about armed forces, assorted federal assets, trade treaties?
Divorce is complicated.
IIRC the problem with China vs. China was that both insisted they were the representative of the entire domain fo China, altho one only de facto controlled Formosa and the other controlled everything else. You can’t admit someone who claims what someone else claims - one has to go. The Nationalist government held the seat (including security council) based on their position when the UN was formed, but it was becoming increasingly obvious that pretending the most populous country in the world was controlled by a rump faction was less and less tenable, and more and more countries were simply accepting reality.
The current Kosovo problem is apparently that there are some predominantly ethnic Serb towns, but in the Serbs boycotted the recent local elections so now the ethnic Kosovo non-Serb candidates won and are taking their mayoral posts (if the local town halls have not been burned down.) NATO troops are there I assume to impress on Serbia the importance of letting Kosovo be Kosovo.
Whether the original annexation of Kosovo or it’s departure are legal, I’m reminded of the quote from Clavell’s Shogun
“There are no ‘mitigating circumstances’ when it comes to rebellion against a sovereign lord.”
“Unless you win.”