So far as I can discover, the territories that now form Belarus have relatively little history as an independent nation, having passed from Russian principalities, to Polish-Lithuanian dominance, to absorption into the Russian Empire and then the USSR.
How did a Belorussian national conscience develop, and why did it emerge as an independent state after the fall of the USSR?
Not to discourage other answers, but you might be interested in this post:
How did Belorussians and Ukrainians evolve as distinct national identities from Russia? with the top answer from /u/cheapwowgold4u.
It's an older post from when AskHistorians allowed wikipedia as a source, but it's a well thought out answer. I'd link more posts but I'm on mobile, but if you search 'Belarus' in the search bar, a good amount of relevant posts come up. Hope that helps!