Crafty-- I think that most wars and other violence are fought for what we'd call economic reasons, not religious ones. One group wants what another has, or is defending their own against others, or wants to dominate trade in some region. A common religion binds a people together, and it's natural for people to use religious rhetoric to rally themselves and make the opposition seem immoral and reduce our inhibitions against fighting them. That doesn't mean that religion is the cause, just a rationalization.
Persians vs Greeks. Alexander the Great's wars of conquest. Romans vs Carthaginians. Roman conquests. All the wars fought by the ancient Chinese. Rome vs Germanic tribes. Huns vs Romans. Viking raids. England vs the Normans. Mongol conquests. England vs Spain. England vs France. A sampling of wars fought over no particular religious principles.
Look at wars in the 20th century. How many of these wars were fought because of religion? Relatively few. Massacres, forced starvations and deprivations, by totalitarian governments, killing millions...how many for religious reasons? Relatively few, and most of those to persecute and eliminate religions, as opposed to based on religious teachings as you said.
War in Iraq...based on religion? Not oil? Not for American hegemony? Not for security concerns? Not for military strategic concerns? Not for internal political reasons in the Western nations? Not to give democracy a foothold in the Middle East? But for religion?
Clashes of religions can make wars and other conflicts more vicious. So can clashes of political ideologies. I think the latter has tremendously more documentation of actually being a root cause of wars and other misery, apart from economics, than religion.
