I've read about Communism, and they weren't persecuting religion to promote atheism, but to promote Communism. ANY religious organization represents an authority not controlled by the state, and that was anathema to the Communists. Sure, they were atheists, some of them. But that had nothing to do with what they were doing to religious groups. They wanted ALL authority to reside within the Supreme Soviet. Worship of the state, and not of gods. It's still a religion, not atheism.