What was Hitler's religious motivation?  Stalin?  Lenin?  Pol Pot?  Mao Zedong?

Atheists have killed as much as religious zealots.

"... you might as well debate what color underpants are worn by the largest number of killers, and try to draw a causal relationship there as well. Religion does not cause you to kill people, and it certainly doesn't prevent you from killing people. "

https://skeptoid.com/episodes/4076