Israel's occupied territories remain "occupied" because they were won in a preemptive war, and nobody would accept that the first to use force could incorporate the territory it won.
During the Nigerian Civil War, almost everyone was willing to watch Biafra fail rather than open the door to a precedent of redrawing borders by force.
The coalition for the first Gulf War was united by a principle that Iraq could not incorporate Kuwait by force.
In Yugoslavia, the consensus began to break. By engaging in "humanitarian intervention" against Serbia and for Kosovo, the US and NATO involved itself in what was essentially a civil war. As a Serbian friend of mine put it at the time, it was a violation of CIL. He was right. What he failed to see (or accept) was that the law was changing.
Now Kosovo declares its independence, and several major powers (including the US) recognize it. As a practical matter, this is less than it appears: KFOR stays in place, the provisional government (set up with the help of the UN) keeps on provisionally governing. As a symbolic matter, it is enormous. Who else is free to declare their independence in response to perceived mistreatment?
Transdenistra is calling for international recognition, claiming Kosovo as a precedent.
Chechnya would of course want a state of its own.
Palestine--a no-brainer. But a two-state solution, or three?
Why shouldn't Muslim territories leave China? And how about independence for Taiwan?
Are there any African states with borders that are even close to the borders of their nations?
How about the Amerindian nations?
Follow this to its logical conclusion, and the world will have thousands of states. And, maybe, that's not such a bad idea. If you like small government (as I do), the best way to keep them small is to keep them divided. But a "velvet divorce" is rare among states. Governments tend to have a fetish about maintaining territorial integrity. Majority nations like to remain in charge of minorities. As the norm for unalterable borders loses legitimacy, we either need a new mechanism to manage the transitions--deciding which are legitimate and which are not--or we'll see even more "interesting times."