112 One section of Socialism has undergone almost the same change that the capitalistic economic system, as We have explained above, has undergone. It has sunk into Communism. Communism teaches and seeks two objectives: Unrelenting class warfare and absolute extermination of private ownership. Not secretly or by hidden methods does it do this, but publicly, openly, and by employing every and all means, even the most violent. To achieve these objectives there is nothing which it does not dare, nothing for which it has respect or reverence; and when it has come to power, it is incredible and portentlike in its cruelty and inhumanity. The horrible slaughter and destruction through which it has laid waste vast regions of eastern Europe and Asia are the evidence; how much an enemy and how openly hostile it is to Holy Church and to God Himself is, alas, too well proved by facts and fully known to all. Although We, therefore, deem it superfluous to warn upright and faithful children of the Church regarding the impious and iniquitous character of Communism, yet We cannot without deep sorrow contemplate the heedlessness of those who apparently make light of these impending dangers, and with sluggish inertia allow the widespread propagation of doctrine which seeks by violence and slaughter to destroy society altogether. All the more gravely to be condemned is the folly of those who neglect to remove or change the conditions that inflame the minds of peoples, and pave the way for the overthrow and destruction of society.
Source: Quadragesimo Anno (Vatican.va)