I must quibble with one remark. Was Joseph Stalin an atheist? I know it's customary to refer to him and Lenin as atheists. Both were brought up as Christians. I've read that Lenin renounced religion and theism in his teens, but I've never read that Stalin ever pronounced himself an atheist. I do know that Stalin attended a seminary in his late teens to become a priest, wrote religious poetry in his 20s and mentioned God favorably to Churchill when he visited Moscow in 1942. Churchill wrote that, when he told Stalin of Operation Torch, the U.S. invasion of N. Africa, Stalin replied that he hoped God would favor the invasion. Stalin also said he left it to God to decide about Churchill's differences with him. So was Stalin an atheist, or merely anti-church? Hitler was a lifelong Christian, but seems to have become hostile to organized religion in his last few years (the sources are not very good on his later beliefs, but an argument can be made that he abandoned key Catholic doctrines, becoming a kind of generic Protestant or even, as some historians argue, a Deist). So claims that two of the worst monsters of the 20th century were atheists are, at best, very dubious and at worst out-right lies on Hitler and unproven for Stalin (unless there's evidence I do no know; I'm not an expert on Stalin).