Never happened. Atheists rarely attain any sort of power whatsoever. Perhaps you are thinkign of the Communists, who were about as atheist as *you* are. They simply replaced a supernatural God with a "historical dialectic" god and a State-god.
Your delusion continues...from wikipedia...http://en.wikipedia.org/wiki/Persecution_of_Christians
An intense ideological anti-Christian and anti-religious campaign was carried out throughout the history of the Soviet Union. An extensive education and propaganda campaign was undertaken to convince people, especially the children and youth, not to become believers. The role of the Christian religion and the Church was painted in black colors in school textbooks. For instance, much emphasis was placed on the role of the Church in such historical horror stories as the Inquisition, persecution of Galileo, Giordano Bruno, and other heretical scientists, and the Crusades. School students were encouraged to taunt and use peer pressure against classmates wearing crosses or otherwise professing their faith. In the 1920s there were many "anti-God" publications and social clubs sponsored by the government, most notably the scathingly satirical "Godless at the Workbench" ("Bezbozhnik u Stanka" in Russian). Later on, these disappeared because a new generation has grown up essentially atheist.
A "scientific" perspective was used to attack religion extensively. The Church was portrayed as obscurantist and opposed to the findings of science. Much was made of alleged Christian belief in the literal Creation account in the book of Genesis which the pro-Darwinian textbooks ridiculed. Interestingly, as part of the anti-foreign and anti-capitalist propaganda, an effort was made, especially in the 1920s and 1930s, to imprint in the minds of the people an image of the West as dominated by the anti-scientific ignorance of the Church, as opposed to the scientifically "progressive" atheist Soviet state.
In general, Christianity was portrayed as corrupt, hypocritical, a loyal servant of the reactionary czar, obscurantist, "opium for the people" according to Karl Marx, and otherwise evil. This Communist persecution of the Church proved enormously successful. Within the span of one generation, the traditionally highly devout Russian people became overwhelmingly atheist. This transformation was, for the most part, complete by the 1950's. As such, it counted as one of the greatest and the most successful persecutions Christianity had ever experienced, on par only with the destruction of Christianity in the Middle East, North Africa, and Asia Minor by the Islamic and Turkish conquests.
> Your delusion continues
I'm sorry, but you went off on a tangent. You never did counter the fact that the Commies weren't actually atheists.