9 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.
Source: Divini Redemptoris (Vatican.va)