34 As often, indeed, as the supreme pontiffs have resisted the most powerful among rulers, in their threatening demands that divorces carried out by them should be confirmed by the Church, so often must we account them to have been contending for the safety, not only of religion, but also of the human race. For this reason all generations of men will admire the proofs of unbending courage which are to be found in the decrees of Nicholas I against Lothair; of Urban II and Paschal II against Philip I of France; of Celestine III and Innocent III against Alphonsus of Leon and Philip II of France; of Clement VII and Paul III against Henry VIII; and, lastly, of Pius VII, that holy and courageous pontiff, against Napoleon I, when at the height of his prosperity and in the fullness of his power. This being so, all rulers and administrators of the State who are desirous of following the dictates of reason and wisdom, and anxious for the good of their people, ought to make up their minds to keep the holy laws of marriage intact, and to make use of the proffered aid of the Church for securing the safety of morals and the happiness of families, rather than suspect her of hostile intention and falsely and wickedly accuse her of violating the civil law.
Source: Arcanum Divinae (Vatican.va)