I sometimes find myself looking up Russian words on wiktionary and following the etymology of the word upstream to find what words it is related to, as you do. I think I've noticed a peculiar thing: in words of the same origin, the Eastern Slavic languages seem to agree pretty well on which one of the syllables is stressed. For example, the corresponding forms of górod are in Belorussian stressed as "hórad", and in Ukrainian, "hórod". There's also "molokó" vs "malakó", etc. It doesn't seem to hold true outside of the Eastern branch, as the Polish form of "zemljá", "zemia", is stressed on the first syllable.
What is the cause of this pattern? Is this an Eastern Slavic thing which they inherited from their most recent common ancestor, did they borrow it from Church Slavonic, or is it simply that Belorussian and Ukrainian have for most of their recent history been treated as Russian dialects and come under heavy Russian influence?
To speakers of the other Eastern Slavic languages, what are some exceptions to the rule?