In international law, certainly in the UN, there is a balance struck between the rights of nations/states, and the rights of people.

Essentially, the balance struck is that a state enjoys complete sovereignty in its territory, etc. as long as it respects the human rights and liberties of the people who live within its borders - ALL the people.

If there is a distinct ethnic or religious population within a state's borders who are being persecuted, then those people whave the right to a referendum and to declare their secession from that state, thereby creating a NEW state for themselves.

As an American, I understand this concept as it was endemic not just to the founding of the USA ("When in the course of human events..."), but also to the founding of the CSA.

The right of a persecuted people deciding to secede and become independent was also a concept endorsed by NATO and the West when they backed Kosovo's secession from Serbia due to oppression of its people in 1999/2008.

Ukraine was persecuting the ethnic Russians living in the Donbas. They refused to accept the coup government imposed by the USA in Kiev, and they formed the DPR and LPR as independent states. Russia recognised those independent states and signed a mutual defense pact with them. The SMO was launched under the auspices of that agreement.