0 ENCYCLICAL OF POPE PIUS XI ON RELIGIOUS UNITY TO OUR VENERABLE BRETHREN THE PATRIARCHS, PRIMATES, ARCHBISHOPS, BISHOPS, AND OTHER LOCAL ORDINARIES IN PEACE AND COMMUNION WITH THE APOSTOLIC SEE. Venerable Brethren, Health and Apostolic Benediction. Never perhaps in the past have we seen, as we see in these our own times, the minds of men so occupied by the desire both of strengthening and of extending to the common welfare of human society that fraternal relationship which binds and unites us together, and which is a consequence of our common origin and nature. For since the nations do not yet fully enjoy the fruits of peace - indeed rather do old and new disagreements in various places break forth into sedition and civic strife - and since on the other hand many disputes which concern the tranquillity and prosperity of nations cannot be settled without the active concurrence and help of those who rule the States and promote their interests, it is easily understood, and the more so because none now dispute the unity of the human race, why many desire that the various nations, inspired by this universal kinship, should daily be more closely united one to another.
Source: Mortalium Animos (Vatican.va)