The Kosovo Precedent is interesting at a slightly more than philosophical level lately.
It is essentially an argument about sovereignty: what defines a nation-state? What do you need to have in order to declare a country? This is not as simple a question as you might think.
"Countries" as we define them today are a relative novelty historically speaking. A country, as a political entity with official presences and leaders, comprised more or less by the consent of the people governed thereby, did not really exist until, I'd argue, 1776 or so, when America was formed.
I don't think a principality or a duchy or a kingdom is a country. It's just... a thing that acts like a country. The difference is whether the country can exist without a change in leadership or governance; it's whether there is a separation between ideology and personal interest, and the official existence of a country.
Thus, if America was run by Communists, at some purely ideological level you could quibble whether or not it was still America, but it would still be, for all intents and purposes, on the world stage and in terms of its official functions, still America. The same would not pertain to a kingdom - thus, when Russia turned Communist, it was no longer a proto-feudalist czarist society, it was something else, something closer to a true nation-state, I'd argue.
The standard definition of sovereignty is something like having exclusive control over violence within a given territory. But this is more like a sufficient than a necessary condition; control of violence within a country can be more or less effective and it doesn't make it more or less of a country. Like, Germany isn't less Germany because its police are struggling with right-wing elements, that just doesn't make sense. I don't think that maps neatly either.
Then you have "countries" like SeaLand - an oil platform in the middle of the North Atlantic that got taken over by some nutcase, staking a claim on essentially nothing. These are barely worth mentioning.
So, the Kosovo Precedent states that all you really need to have a country and not, like, SeaLand, is to have recognition by a third party who can guarantee your sovereignty.
It's based on what happened to Kosovo. It is a slight oversimplification, but only a slight one, to state that Kosovo is a country that NATO bombed and recognized into existence.
Russia backed the Serbs in that conflict, and they generally grandly dislike NATO, so they took the Kosovo Precedent very, very seriously. We know this from statements by Putin as well as by what happened immediately after.
Russia "recognized" a relatively dinky little country called South Ossetia which happened to be inside the borders of its neighbor, Georgia, invaded it, then essentially annexed it, using the Kosovo Precedent as a pretext.
On Russia's account, it wasn't an invasion or annexation - it was a guarantee of sovereignty for a putative independent state.
If this sounds slightly reminiscent of something you've heard recently about Ukraine, you're right: it is. This is the same rationale that Russia cited in the late February for the Ukraine war - a putative assertion of sovereignty for two breakaway "republics", in reality separatist provinces of Ukraine.
Again, it goes back to the Kosovo Precedent, and the question of, what makes a country?
Is it control of force within its boundaries? What if that control of force is propped up by a third party, entirely like NATO and Kosovo, or the early days of Israel? What if only the head of state is propped up, like Belarus?
What if only one faction or tribe is being propped up, like Ramzan Kadyrov and Chechnya? Is that still a security guarantee sufficient to make an actual country, and not just an entity going through the motions?
This is really much more complicated in the historical view than it needs to be; I can understand if this seems slightly overwhelming to people. Again, we can make it very unambiguous and simple.
What the question boils down to, in the Minsk II Agreement and the so-called Donetsk and Luhansk People's Republics in Ukraine is this:
Are lying and killing by a third party (Russia) sufficient to establish a country?
I don't know that 100%. But right now, my answer would probably be "not if Ukraine has anything to say about it".