Is this the only possible measure of a relationship between religion and violence? What was the co-religionist murder rate among Bhuddists in 700 AD relative to the murder rate among Muslims or Christians? I’m not saying it was higher or lower, but I can illustrate some of the complexities in trying to analyze what it means for a religion to be “more violent.” Political religious violence in antiquity is deeply tied to the spread of empire. To gain imperial territory and to spread a religion were practically synonymous for many civilizations–though not all. In practical terms Buddhism spread through conversion of elites who continued to use violence, and its spread was connected to the violence intrinsically connected to power. Just like most ancient religions. Of course, many more empires were explicitly Christian or Islamic than Buddhist, and Buddhism didn’t seem to be a significant barrier to violence for those Buddhist empires that did exist. If a religion cannot prevent violence by having more adherents, can it be said to be less violent? Chinese history is hardly one of non-violence.
Meanwhile many of the wars you can cite as being inherently religious had numerous ulterior motives than aren’t always extricable from religious ideas and philosophies for the same reasons it’s possible for a Buddhist like you to condemn concentration camps in Sri Lanka while others justify them in the name of Buddhism. This kind of complexity isn’t unique to the 21st century-- why would it be? What accounts for that exception crossing the 20th century mark? Were previous Buddhists more pure? I doubt it very much.
Many early Islamic conquests were similar to Mongol conquests very early on. Arabs tended to live in pastoral and nomadic communities and empire was managed by delegation with little concern for immediate conversion. The importance of conversion as a mechanic in Islam to create imperial specialization and class-structures is very well studied and is the subject of a great deal of scholarship. Look into how many Muslim elites didn’t like conversion because it diluted their power. It’s some really interesting counter-intuitive stuff. So how do we analyze the violence of subjecting people to class structure while simultaneously discouraging conversion with certain kinds of incentives and concessions? Is that about Islam? Or is that about power? Or is it about both?
There are nuances here, and declarations of war didn’t come on a form with a section titled “Reason:” and a tick box for “Religious conversion.” It was always more complicated than that. For Buddhists and everyone else.