122 Since in Our Encyclical, The Christian Education of Youth , We have fully taught the principles that Christian education insists on and the ends it pursues, the contradiction between these principles and ends and the activities and aims of this socialism that is pervading morality and culture is so clear and evident that no demonstration is required here. But they seem to ignore or underestimate the grave dangers that it carries with it who think it of no importance courageously and zealously to resist them according to the gravity of the situation. It belongs to Our Pastoral Office to warn these persons of the grave and imminent evil: let all remember that Liberalism is the father of this Socialism that is pervading morality and culture and that Bolshevism will be its heir.
Source: Quadragesimo Anno (Vatican.va)