The Truth About the Catholic Church and Slavery

from Christianity Today:
Nothing ambiguous here. The problem wasn't that the Church failed to condemn slavery; it was that few heard and most of them did not listen. In this era, popes had little or no influence over the Spanish and the Portuguese since at that time the Spanish ruled most of Italy; in 1527, under the leadership of Charles V, they had even sacked Rome.

As Eugene Genovese put it: "Catholicism made a profound difference in the lives of the slaves. [It] imparted to Brazilian and Spanish American slave societies an ethos…of genuine spiritual power."