1 The maternal love of the Catholic Church embraces all people. As you know,venerable brother, the Church from the beginning sought to completely eliminateslavery, whose wretched yoke has oppressed many people. It is the industriousguardian of the teachings of its Founder who, by His words and those of theapostles, taught men the fraternal necessity which unites the whole world. FromHim we recall that everybody has sprung from the same source, was redeemed bythe same ransom, and is called to the same eternal happiness. He assumed theneglected cause of the slaves and showed Himself the strong champion of freedom.Insofar as time and circumstances allowed, He gradually and moderatelyaccomplished His goal. Of course, pressing constantly with prudence andplanning, He showed what He was striving for in the name of religion, justice,and humanity. In this way He put national prosperity and civilization in generalinto His debt. This zeal of the Church for liberating the slaves has notlanguished with the passage of time; on the contrary, the more it bore fruit,the more eagerly it glowed. There are incontestable historical documents whichattest to that fact, documents which commended to posterity the names of many of Our predecessors. Among them St. Gregory the Great, Hadrian I, Alexander III, Innocent III, Gregory IX, Pius II, Leo X, Paul III, Urban VIII, Benedict XIV, Pius VII, and Gregory XVI stand out. They applied every effort to eliminate the institution of slavery wherever it existed. They also took care lest the seeds of slavery return to those places from which this evil institution had been cut away.
Source: Catholicae Ecclesiae (Vatican.va)