In the world in which the church was born slavery was ubiquitous and endemic. Roman and Greek society thrived on it, and the Germanic tribes who inherited Roman power were not significantly different in their attitudes. So what was Christian theology to make of a situation that it did not like, which it could not control and which seemed very unloving to one’s neighbour?
Most mediaeval theologians followed the views of Gregory Nazianzen, one of the three Cappadocian Fathers, who in the fourth century argued that all people were naturally free, but that slavery had entered the world through the sin of Adam, which we call original sin. However, his fellow Cappadocian, Gregory of Nyssa, had in 385 preached the first known anti-slavery sermon. Whether any of the rich slave owners listened is not known. Probably some did, but others would not have changed.
Thomas Aquinas, the great Scholastic thinker, writing in the thirteenth century, argued that slavery was a natural evil . However, he allowed that it might be imposed as penalty for crime and was the natural fate of captives in a just war. Like all mediaeval theologians, though, Aquinas favoured the redemption of captives. so captives in a just war should be redeeemed by their countries or merciful captors.
Aquinas’ fellow Scholastic, John Duns Scotus, writing a few years after Aquinas, took issue with the interpretation of certain apparently pro-slavery passages in the First Letter of Peter, one of the New Testament letters. Peter argues that slaves should obey their masters, but that masters should treat them well. Scotus argued that the apostle was trying to make the best out of a bad situation. He was probably right. A direct church attack on slavery would have been impossible at the time at which that letter was written, the period of the Neronic persecution of the church in the sixties, when the situation of Christians was dire.
The mediaeval papacy has an unjustly bad press, as it is commonly thought that all these popes self-indulgent villains. Some were, but there were also good popes who tried to run the church well. Generally the villains were elected trhough the interference of powerful kings and aristocrats able to enforce their will on the papal election.
Popes varied in their attitudes to slavery .The year 595 saw Gregory the First [the great] the pope famous for sending St Augustine to convert the English, enact a document freeing slaves, in which he taught that humans were naturally free and therefore captives should be liberated. In 873 John the Eighth wrote to the princes of Sardinia ordering that those who had unjustly taken slaves should liberate them. Whether they obeyed is not certain.
In 1435 Eugenius the Fourth issued edicts ordering the Spanish conquerors of the Canary Islands to liberate the native Guanches whom they had enslaved. The trouble is that the pope was some geographical distance from the people to whom he was giving the orders, and it was hard for him to enforce his will. In addition, he had only words, but not weapons.
The Clash with Islam
Yet not all popes are as impressive as these three, probably because some were linked to powerful political and economic interests.Most were content to keep church teaching as it was, accepting that previous papal statements had made the necessary points. In 1452, however, Nicholas the Fifth, who wanted a united front against Islam, conceded to the Portugese that they could capture Saracens and pagans, even perpetually enslaving them. This was the political price that he was to pay for his anti-Islam strategy. Ten years later Pius the Second condemned those who took new Christian [black] converts into slavery, but added nothing to what previous popes had said.
The situation that prevailed in Europe in the later Middle Ages was that Christianity was under siege from Islamic forces. The Muslims were taking European/Christian slaves in abundance, so the Europeans replied by capturing Muslims. The European feeling was that Muslim captives were taken in a just war so could be enslaved. The North African and Turkish practice of capturing European, Christian slaves only ended in the nineteenth century because European forces managed to defeat the slave-taking states.
Generally monasteries did not own slaves. Certain religious orders, however, arose with the specific purpose of liberating Christian slaves from the Muslims. These included the Trinitarian order, which was founded in the early thirteenth century. Its full title is the Order of the Holy Trinity and Captives. Trinitarians used to tour Europe, preaching in churches to solicit funds for the liberation of Christain slaves. They developed a system of contacts with the Muslim world through which the funds for liberation would be channelled.
The Mercedarians were a lay religious order. This means that they did not contain ordained priests or monks, but they were ordinary people who lived in the world , but followed a religious rule of life. they were committed to soliciting funds for the redemption of Christian slaves from the Muslims. Founded in 1218, they ransomed poor people whose families were unable to provide funds for themselves. Both of these orders still exist, though their remit has adapted over the years to wider forms of service. Much of their work was in the Mediterranean region, where the capturing of European slaves was a common practice.