2 Words, then, are not required to show how great need they have of being illuminated from on high that they may carry out their great task well. And, as their decisions will be of supreme interest to all humanity, there is no doubt that Catholics, for whom the support of order and civil progress is a duty of conscience, must invoke Divine assistance for all who take part in the peace conference. We desire that that duty be brought before all Catholics. Therefore, Venerable Brothers, in order that there may come from the Congress shortly to be held that great gift of heaven, true peace founded on the Christian principles of justice, that enlightenment from the Heavenly father may descend on them, it shall be your care to order public prayers in each parish of your dioceses in the way you may think most convenient. As for Us, representing, however unworthily, Jesus Christ, King of Peace, We shall exert all the influence of Our Apostolic Ministry that the decisions which are to be taken to ensure for ever in the world the tranquility of order and concord be willingly accepted and faithfully carried out by Catholics everywhere.
Source: Quod Iam Diu (Vatican.va)