Sadly we, the "good guys", created a dangerous precedent in the balkans when Kosovo unilaterally split from Serbia, under foreign (NATO) occupation moreover.
International law does not promote nor support unilateral secessions. If a region or autonomous republic wants to secede it should only do so in accordance to the host country laws. E.g. the Quebec and Scotland referendums were made in accordance to the host countries of Canada and UK.
But then we created that dangerous case where now every region can secede from their host one unilaterally, even if it's occupied by foreign forces. And in practice, the "legality" of it, really depends on international recognition and the undergoing narratives.
International laws have always been pleasantries, as there's no real ways to enforce them, but there were powerful incentives for everybody to play by the rules.
It's hardly a precedent, probably half of the countries worldwide have been formed by seceding from some other country against its will. U.S. would be in this half.
It's the first country to do so under foreign military presence since UN inception.
The only precedents of unilateral secession were Slovenia and Croatia from Yugoslavia and Bangladesh from Pakistan but none did so under foreign military presence.
All of the Arab countries have basically seceded from Ottoman empire under an occupation of this or that European country.
"Unilaterally" is not easy to define. Sometimes there is a long and violent struggle for independence and the metropole eventually gives in and signs some paper, sometimes it is stubborn and doesn't sign anything - the difference is not that important in my opinion.
International law does not promote nor support unilateral secessions. If a region or autonomous republic wants to secede it should only do so in accordance to the host country laws. E.g. the Quebec and Scotland referendums were made in accordance to the host countries of Canada and UK.
But then we created that dangerous case where now every region can secede from their host one unilaterally, even if it's occupied by foreign forces. And in practice, the "legality" of it, really depends on international recognition and the undergoing narratives.
International laws have always been pleasantries, as there's no real ways to enforce them, but there were powerful incentives for everybody to play by the rules.