From Divini Redemptoris (On Atheistic Communism) in 1937;
“The promise of a Redeemer brightens the first page of the history of mankind, and the confident hope aroused by this promise softened the keen regret for a paradise which had been lost. It was this hope that accompanied the human race on its weary journey, until in the fullness of time the expected Savior came to begin a new universal civilization, the Christian civilization, far superior even to that which up to this time had been laboriously achieved by certain more privileged nations.
2. Nevertheless, the struggle between good and evil remained in the world as a sad legacy of the original fall. Nor has the ancient tempter ever ceased to deceive mankind with false promises. It is on this account that one convulsion following upon another has marked the passage of the centuries, down to the revolution of our own days. This modern revolution, it may be said, has actually broken out or threatens everywhere, and it exceeds in amplitude and violence anything yet experienced in the preceding persecutions launched against the Church. Entire peoples find themselves in danger of falling back into a barbarism worse than that which oppressed the greater part of the world at the coming of the Redeemer.
3. This all too imminent danger, Venerable Brethren, as you have already surmised, is bolshevistic and atheistic Communism, which aims at upsetting the social order and at undermining the very foundations of Christian civilization .
4. In the face of such a threat, the Catholic Church could not and does not remain silent.” read Divini Redemptoris online