14 Various political governments have succeeded one another in France during the last century, each having its own distinctive form: the Empire, the Monarchy, and the Republic. By giving one's self up to abstractions, one could at length conclude which is the best of these forms, considered in themselves; and in all truth it may be affirmed that each of them is good, provided it lead straight to its end - that is to say, to the common good for which social authority is constituted; and finally, it may be added that, from a relative point of view, such and such a form of government may be preferable because of being better adapted to the character and customs of such or such a nation. In this order of speculative ideas, Catholics, like all other citizens, are free to prefer one form of government to another precisely because no one of these social forms is, in itself, opposed to the principles of sound reason nor to the maxims of Christian doctrine. What amply justifies the wisdom of the Church is that in her relations with political powers she makes abstraction of the forms which differentiate them and treats with them concerning the great religious interests of nations, knowing that hers is the duty to undertake their tutelage above all other interests. Our preceding Encyclicals have already exposed these principles, but it was nevertheless necessary to recall them for the development of the subject which occupies us to-day.
Source: Au Milieu Des Sollicitudes (Vatican.va)