You are correct that what I said could just reflect the fact that Buddhism hasn't reached the same level of political consolidation as Christianity. But there have been Buddhist empires throughout history.

You do point out another aspect that I was reflecting on though, that these religions are used as tools by nationalists or other political authorities. In my view it is not the religion itself that enables or supports these atrocities but the centralized power that these organizations are able to hold. Human societies have had religion for all of known history so it is difficult to thoroughly prove that these societies would be more or less violent without religion of any type. If they didn't have a religious group driving the masses to be pawns of their violence, it could be a trade group like the Dutch East India Company.