We flipped the finger to the UN and international law ref initiation of war. We signed that agreement and there was no exception in the case you can get the EU or NATO to join you in whatever plot you are hatching.
I don’t really care about getting permission from the UN. But please don’t act like Russia did something shocking by not seeking UN approval. We bombed Serbia for 78 days without that.
The US did not invade Serbia. Russia invaded Ukraine, and did so with precisely the excuses Hitler used to invade Poland. That is the beginning and end of the story about legitimacy of action.