I used to think that England was a bully for swallowing Wales, Scotland, Cornwall, and Ireland. What justification was there? I think the Ukraine War answers that question.
If Wales had been completely independent of England, Wales might have made agreements with France (or other enemies of England) to use Wales as a springboard for attacking England. The resulting war would have been bloody because France would have gotten entrenched on the island of Britain.
Likewise Russia made a mistake in allowing Ukraine to join Russia's enemies after the 2014 coup d'état. The bloodiness increased because of that decision. You could probably make the same argument about Russia allowing the Baltic countries, Poland, or Finland to join Russia's enemies, unless Russia permanently accepts these changes. But it couldn't accept Ukraine allying itself with Russia's enemies.