The Iberian Connection- page 11?
For the Portuguese, a moral argument justifying the enslavement of the Moors had not been necessary. A war against Islam was an unalloyed battle against evil and, therefore, was innately righteous. Even the slavery of white Christians was a long-time tradition in Iberia and, although the Catholic church gradually adopted an intransigently hostile position toward it, the practice continued. It was adjudged a phenomenon involving unfortunate individuals rather than races, and if an individual succeeded in emancipating himself, he could become a full-fledged member of society.
Justification for the enslavement of sub-Saharan Africans lay in papal bulls issued by Nicholas V (1454) and Calixtus III (1456). These documents established Lisbon?s drive down the western cost of Africa as a crusade and intimated that the enslavement of pagans was beneficial since they could then be Christianized. The papal pronouncements in this last regard did not represent a marked departure from generally held beliefs. As early as 1444, for example, in accepting his share of captives from Lancarote de Freitas?s raid, Prince Henry had suggested that slavery was not an outrageous price for the African to pay for his Christianization.
--Excerpt from The Afrikan Experience in Spanish America.