5 During Our Pontificate We too have frequently and with urgent insistence denounced the current trend to atheism which is alarmingly on the increase. In 1924 when Our relief-mission returned from the Soviet Union We condemned Communism in a special Allocution which We addressed to the whole world. In our Encyclicals Miserentissimus Redemptor , Quadragesimo Anno , Caritate Christi , Acerba Animi , Dilectissima Nobis, We raised a solemn protest against the persecutions unleashed in Russia, in Mexico and now in Spain. Our two Allocutions of last year, the first on the occasion of the opening of the International Catholic Press Exposition, and the second during Our audience to the Spanish refugees, along with Our message of last Christmas, have evoked a world-wide echo which is not yet spent. In fact, the most persistent enemies of the Church, who from Moscow are directing the struggle against Christian civilization, themselves bear witness, by their unceasing attacks in word and act, that even to this hour the Papacy has continued faithfully to protect the sanctuary of the Christian religion, and that it has called public attention to the perils of Communism more frequently and more effectively than any other public authority on earth.
Source: Divini Redemptoris (Vatican.va)