The doctrine of modern Communism, which is often concealed under the most seductive trappings, is in substance based on the principles of dialectical and historical materialism previously advocated by Marx, of which the theoricians of bolshevism claim to possess the only genuine interpretation. According to this doctrine there is in the world only one reality, matter, the blind forces of which evolve into plant, animal and man. Even human society is nothing but a phenomenon and form of matter, evolving in the same way. By a law of inexorable necessity and through a perpetual conflict of forces, matter moves towards the final synthesis of a classless society. In such a doctrine, as is evident, there is no room for the idea of God; there is no difference between matter and spirit, between soul and body; there is neither survival of the soul after death nor any hope in a future life. Insisting on the dialectical aspect of their materialism, the Communists claim that the conflict which carries the world towards its final synthesis can be accelerated by man. Hence they endeavor to sharpen the antagonisms which arise between the various classes of society. Thus the class struggle with its consequent violent hate and destruction takes on the aspects of a crusade for the progress of humanity. On the other hand, all other forces whatever, as long as they resist such systematic violence, must be annihilated as hostile to the human race.
What would be the condition of a human society based on such materialistic tenets? It would be a collectivity with no other hierarchy than that of the economic system. It would have only one mission: the production of material things by means of collective labor, so that the goods of this world might be enjoyed in a paradise where each would “give according to his powers” and would “receive according to his needs.” Communism recognizes in the collectivity the right, or rather, unlimited discretion, to draft individuals for the labor of the collectivity with no regard for their personal welfare; so that even violence could be legitimately exercised to dragoon the recalcitrant against their wills. In the Communistic commonwealth morality and law would be nothing but a derivation of the existing economic order, purely earthly in origin and unstable in character. In a word. the Communists claim to inaugurate a new era and a new civilization which is the result of blind evolutionary forces culminating in a humanity without God. Pius XI: Atheistic Communism