Pope Paul not only condemned the slavery of Indians but also "all other peoples." In his phrase "unheard of before now", he seems to see a difference between this new form of slavery (i.e. racial slavery) and the ancient forms of just-title slavery. A few days before, he also issued a Brief, entitled Pastorale Officium to Cardinal Juan de Tavera of Toledo, which warned the Catholic faithful of excommunication for participating in slavery.
Unfortunately Pope Paul made reference to the King of Castile and Aragon in this Brief. Under political pressure, the Pope later retracted this Brief but did not annul the Bull. It is interesting to note that even though he retracted his Brief, Popes Gregory XIV, Urban VIII and Benedict XIV still recognized and confirmed its authority against slavery and the slave trade.
Popes Gregory XIV (Cum Sicuti, 1591), Urban VIII (Commissum Nobis, 1639) and Benedict XIV (Immensa Pastorum, 1741) also condemned slavery and the slave trade. Unlike the earlier papal letters, these excommunications were more directed towards the clergy than the laity. In 1839, Pope Gregory XVI issued a Bull, entitled In Supremo. Its main focus was against slave trading, but it also clearly condemned racial slavery:
We, by apostolic authority, warn and strongly exhort in the Lord faithful Christians of every condition that no one in the future dare bother unjustly, despoil of their possessions, or reduce to slavery Indians, Blacks or other such peoples. [Ibid., pp.101]
Unfortunately a few American bishops misinterpreted this Bull as condemning only the slave trade and not slavery itself. Bishop John England of Charleston actually wrote several letters to the Secretary of State under President Van Buren explaining that the Pope, in In Supremo, did not condemn slavery but only the slave trade (Ibid., pp. 67-68).
With all these formal condemnations, it is a shame that the Popes were largely ignored by the Catholic laity and clergy. Two Catholic nations were largely involved with slave trafficking. Many Catholics at that time owned or sold slaves. Even some Catholic bishops during the 19th-century appeared to support slavery. The Popes were so ignored that some people today claim that they were silent. These sins brought great scandal to Christís Church.