I'm Polish, out of my 8 grandfathers: 2 come from modern day central Ukraine (Vinnytsia), 2 come from modern day Belarus (Ashmyany).
It's very hard to explain to people how weak the whole concept of nation state used to be in Eastern Europe till ww2.
From Eastern Germany to the Urals, every place you would go it was a deeply cosmopolitan mix of Germans, Jews, different Slav ethnicities and depending on the regions significant Romanians, Hungarians, Turks and some other minorities.
You would cross from one village to the other and the language would change, and in minor centers neighborhood and districts changed architecture and language. Different ethnicities also generally mapped to different professions and status. And those changes didn't really look like gradients, more like dispersed bubbles.
Ethnic tensions were always present, everybody literally hated and tolerated each other with Jews generally being the common scape goat.
My grandparents coming from modern day Ukraine vividly remember the violence and terror caused by UPA, the nazi-sympathizing Ukrainian militias. My mother's grandma could not forget till the day she lived (died in 2004) what she saw in her childhood village when Ukrainians came and started a massacre that saw her losing a brother, countless cousins, uncles and friends.
Of course, Poles have been the aggressors too, just a few decades before, when Poland attacked the Soviet Union in the 1920s and had its own share of ethnic violence against Ukrainians and Belarusians.
In any case, Eastern Europe is deeply plagued and poisoned by all of this past violence. No one is able to have a mea culpa moment, no one is able to admit their own guys were bloody murders often killing thousands of people like cattle. No one can admit their ancestors crap.
The same happens in the Russo-Ukrainian conflict. The Russians see in Ukrainians the accomplice of their biggest trauma (the Great Patriotic War against Nazi Germany).
The Ukrainians see in Russia the perpetrator of their biggest trauma (the 1920s Holodomor).
No side ever says sorry, no side ever takes responsibility, no side can move on. And Eastern Europe keeps being unhealed from its traumas and carrying this in modern age.
And a man that would rather see the world burn than step out (Putin) plays on those traumas he very well understands for his own personal lust of power.