Im not sure about hitler but it`s a well known fact that the soviet union persecuted christians, they used to put them in mental asylums if they refused to give up there faith....or send them to labour camps and in some cases just kill them.
also look at china religious freedom is forbidden by the state and what christianity is allowed to be practiced is the one sanctioned by the chinese government..did you know that the book of revelations is banned in china.
Im not sure that these people did those things on the basis that they truly believed there was no God, but there actions all point to the fact that they where so hungry for power and controlle that they wanted to stamp out God altogether....so in that regard they are athiests because they had no belief in God.
peace be with you !
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