61 At the beginning of industrialized society, it was "a yoke little better than that of slavery itself" which led my Predecessor to speak out in defence of man. Over the past hundred years the Church has remained faithful to this duty. Indeed, she intervened in the turbulent period of class struggle after the First World War in order to defend man from economic exploitation and from the tyranny of the totalitarian systems. After the Second World War, she put the dignity of the person at the centre of her social messages, insisting that material goods were meant for all, and that the social order ought to be free of oppression and based on a spirit of cooperation and solidarity. The Church has constantly repeated that the person and society need not only material goods but spiritual and religious values as well. Furthermore, as she has become more aware of the fact that too many people live, not in the prosperity of the Western world, but in the poverty of the developing countries amid conditions which are still "a yoke little better than that of slavery itself", she has felt and continues to feel obliged to denounce this fact with absolute clarity and frankness, although she knows that her call will not always win favour with everyone. One hundred years after the publication of Rerum novarum, the Church finds herself still facing "new things" and new challenges. The centenary celebration should therefore confirm the commitment of all people of good will and of believers in particular.
Source: Centesimus Annus (Vatican.va)