The UN has written in its Charter, that every group of people can make a nation out of its land if they want. Ukraine tried to stop the people of the areas of Luhansk, Donetsk, Kherson, Zaporizhzhia, Donbas, and Crimea (and maybe others) from making their own lands into their own States.
So did Chechens, yet there was no outside intervention and Russia kept attacking until they forced the country into submission. But that's not the only group of people that wanted their own country in the last 50 years. So did the Basques in Spain, Frisians in the Netherlands, Kosovo and many many more.
How can these countries ignore the UN? Russians like to intervene when they can to help protect people's right to have their own country. They're so helpful and protective. For instance, when part of Moldova wanted to form their own country called Transnistria, Russia had to
helpcome in, and just like in Ukraine took the side of separatists against Moldova. The goal was to weaken the country, because that's what Russians like to do. They want to incite conflicts withing the borders of their neighbors. Haven't you noticed that whenever a country near Russia faces a problem with separatists, Russians run in to help, but whenever a separatist movement forms in Russia, they threaten everyone with nukes, so nobody dares to come in and Russians destroy the opposition.