The Truth About the Catholic Church and Slavery
With the successful Spanish and Portuguese invasions of the New World, enslavement of the native peoples and the importation of Africans ensued, and some slavers offered the rationale that this was not in violation of Christian morality, as these were not "rational creatures" entitled to liberty but were a species of animals and therefore legitimately subject to human exploitation. This theological subterfuge by slave-traders was artfully used by Norman F. Cantor to indict Catholicism: "The church accepted slavery…in sixteenth-century Spain, Christians were still arguing over whether black slaves had souls or were animal creations of the Lord." Cantor gave no hint that Rome repeatedly denounced New World slavery as grounds for excommunication.
But that is precisely what Pope Paul III (1534 to 1549) had to say about the matter. Although a member of a Roman ecclesiastical family, and something of a libertine in his early years (he was made a cardinal at twenty-five but did not accept ordination until he was fifty), Paul turned out to be a very effective and pious pope who fully recognized the moral significance of Protestantism and initiated the Counter-Reformation. His magnificent bull against New World slavery (as well as similar bulls by other popes) was somehow "lost" from the historical record until very recently. I believe this was due to the extreme Protestant biases of historians, who may also have been scornful of the pope's predicating his attack on the assumption that Satan was the cause of slavery:
[Satan,] the enemy of the human race, who always opposes all good men so that the race may perish, has thought up a way, unheard of before now, by which he might impede the saving word of God from being preached to the nations. He has stirred up some of his allies who, desiring to satisfy their own avarice, are presuming to assert far and wide that the Indians of the West and the South who have come to our notice in these times be reduced to our service like brute animals, under the pretext that they are lacking in the Catholic faith. And they reduce them to slavery, treating them with afflictions they would scarcely use with brute animals.
Therefore, We…noting that the Indians themselves indeed are true men…by our Apostolic Authority decree and declare by these present letters that the same Indians and all other peoples—eventhough they are outside the faith…should not be deprived of their liberty or their other possessions…and are not to be reduced to slavery, and that whatever happens to the contrary is to be considered null and void. (My italics)
In a second bull on slavery, Paul imposed the penalty of excommunication on anyone, regardless of their "dignity, state, condition, or grade…who in any way may presume to reduce said Indians to slavery or despoil them of their goods."