I already referenced Northern Ireland, which was actually Christian vs. Christian, but fighting and killing nonetheless. Grant you, that was killing over religion. As for WWII, didn't the rounding up of Jews into concentration camps come years after Hitler started invading neighboring countries (in 1939, as I recall), which actually started that war, not the killing of Jews. That came later (though that is mostly what WWII was known for).
How about the traditional warring of tribes in Africa upon other tribes? Could that be considered based upon religious differences, or was it more territory and dominance? Outside the wars U.S. has been involved in, or the Arab-Isreali conflicts, I think a lot of man-killing-man during the past 100+ years occurred in Africa, but I don't know that it was primarily over religion.
Regarding your earlier comment, that most non-natural killing of man has been over religion . . would "accidents" be considered "natural"? Seems that an awful lot of people world-wide have been killed due to accidents. Or crime. A lot of people have been murdered in commission of crimes. I don't think most of those killings were due to religion.
Maybe if we go back several centuries, I think it could be true that many people were killed over religious differences. I certainly wouldn't discount all the deaths during the past 40+ years that occurred from fighting in the Middle East. But otherwise, I think the role of religion in killings in recent centuries has not been all that great. Your turn.