In many cases, that alone is enough to be a force driving for unification.
Well, one “brotherly help” from Russians was enough to cause so much fucking damage that we’re not over it 30 years after it ended.
We have more cultural similarities with Germans or Austrians than we do with Russians. To the point that if you visit Vienna you could easily mistake it for Prague (not taking landmarks into account, of course).
I have no common identity with Russians. Yeah, our languages share the same roots, but that’s all.
All the talk about unification of Slavs is one of the reason nobody likes Russians. No, thank you, we already are in a union (EU) and generally speaking, it’s a much better deal, because we share actual history (good and bad) instead of language roots and a few decades of being occupied (and murdered) by Russians.