I've had many, all of which you missed.
(And atheism isn't even necessary in a communist nation to begin with. There's no corrleation.)
Beeep!!! Sorry, wrong answer.
Modern twentieth-century Communism is based on the theories of Karl Marx. Marx considered atheism as a key part of communism, and is famous for saying, "Religion ... is the opium of the masses." Marx was himself an atheist, of course, and he also wrote, "Communism begins from the outset with atheism; but atheism is at first far from being communism; indeed, that atheism is still mostly an abstraction."
Vladimir Lenin wrote: "A Marxist must be a materialist, i. e., an enemy of religion, but a dialectical materialist, i. e., one who treats the struggle against religion not in an abstract way, not on the basis of remote, purely theoretical, never varying preaching, but in a concrete way, on the basis of the class struggle which is going on in practice and is educating the masses more and better than anything else could."
In 1955, Chinese communist leader Chou En-lai declared, "We Communists are atheists".
If you can't believe the Communists themselves, who CAN you believe? Well, how about someone who lived and suffered under Communism?
"Over a half century ago, while I was still a child, I recall hearing a number of old people offer the following explanation for the great disasters that had befallen Russia: "Men have forgotten God; that's why all this has happened. Since then I have spent well-nigh 50 years working on the history of our revolution; in the process I have read hundreds of books, collected hundreds of personal testimonies, and have already contributed eight volumes of my own toward the effort of clearing away the rubble left by that upheaval.
But if I were asked today to formulate as concisely as possible the main cause of the ruinous revolution that swallowed up some 60 million of our people, I could not put it more accurately than to repeat: "Men have forgotten God; that's why all this has happened." - Aleksandr Solzhenitsyn
It's not an accident that every society that has ever started out to be Communist either abandoned it early, or ended up persecuting religion.