Where does Russia's attack of Ukraine fits within this?
According to West, not allowed. However, the West does not exist anymore, and we have two different ideological camps within it. According to USA, it’s bad, but it did not hurt American interests, so a good deal is possible. According to EU, foreign policy of which is hijacked by Baltic right, it is still not allowed, but… Deep currents indicate that as soon as it’s done with formal condemnations, it is desirable that business will resume as usual.
If you're genuinely curious dig into the protests 2014, who won the election, who asked her supporters to take to the streets, and what has she been advocating for for a long time before.
It's all about Crimea and the black sea fleet and pipelines. Every time the same conflict, as Orwell put it: We've always been at war with Eurasia.
Edit: Instead of down-voting, tell me where I'm wrong. All of the facts are public information and you won't even have to leave Wikipedia.