Without going into history too much (who had moral right to a territory, who was where first and so on...), from the legal aspect the parallel is evident. Yugoslavia was recognized as a single country after ww2, and the internal borders were created later, as borders of administrative divisions. When tensions started to brew, ultimately the international community (represented by the West at the time, as Russia was impotent and China shied away from international crisis) that those administrative borders were sancrosanct. Those administrative lines would become state borders. One might say the legal principle was set.

After less than a decade, the principle was broken with Kosovo independence. But there was a caveat, namely that by committing various atrocities against the population of Kosovo, Serbia has lost the right to that part of its territory. So, the spin was that the principle wasn't really broken because there was a more important principle to be upheld, namely stopping an ongoing genocide.

From the legal point of view, the entire intervention in 1999 was illegal. There was no consensus in the UN, it was a unilateral decision by NATO. Even NATO statute was ignored, which states that NATO can not be used in an offensive manner. So, attacking a sovereign country that didn't attack or even threaten to attack a NATO member was obviously an illegal action, but the spin was that NATO wasn't really attacking - it was proactively defending Kosovo Albanians. The moral need for intervention was so great, that it superseded any and all laws.

I would have liked to have seen what legal hoops the judges of ICJ would have had to jump through to absolve NATO from blame if Serbia hadn't withdrawn the lawsuit against 8 NATO members.

Russia is doing the same thing now, maintaining that they haven't really broken any laws or treaties because Crimeans decided to secede from Ukraine in a plebiscite. Again, there's a facade of legality, but even if somebody were to question the legality, the moral imperative was so strong that it superseded everything else - people of Crimea simply couldn't have been left to Nazis in Kiev.

As there isn't an international court that can enforce its decisions in the entire world, the bottom line is the we're still in the "might makes right" territory, regardless of how civilized we like to present ourselves, although no one is willing to admit it.