Alexander the Great is estimated to have executed a million people, same with Genghis Khan.
11th century Crusades killed half a million Jews and Muslims. The Aztecs once slaughtered 100,000 prisoners over four days.
An unknown number, probably in the millions, died in the Devil's Wind action in Colonial India.
Up to four million Hindus, Sikhs, and Muslims died in post-Colonial India.
Pol Pot was raised as a Buddhist monk; he murdered 1,5 million people.
The Ottoman Empire massacred two million Armenians over the years. A hundred thousand people died in Franco's Civil war.
A million people have died in Rwanda, half a million people in Darfur. The Aztecs once slaughtered 100,000 prisoners over four days. Violence between Christians and Muslims has obviously dominated our headlines for a decade, totalling somewhere in seven figures.
43,000 Rohingya are missing presumed dead after being forced to flee their homes.
There is speculation that Hitler may have been a Christian, his own writing suggests a that he sympathized with Muslims. He also used religious imagery.
I'm sure there are examples I haven't thought of.