In AI encyclical, Pope Leo moves church's needle on slavery, just war

In a striking mea culpa, Leo acknowledged the ways in which the Holy See, "responding to requests from Sovereigns, intervened several times in order to regulate and legitimize forms of subjugation, and, in certain cases, the enslavement of 'infidels.'"

Several papal bulls issued amid waves of colonization in the 15th-century explicitly authorized the enslavement of non-Christians by Portuguese rulers. It was not until 1839 that Pope Gregory XVI called that slave trade "inhuman" and "unworthy of the Christian name." The pope's namesake, Pope Leo XIII, later issued an encyclical on the abolition of slavery in 1888.

Leo XIV, who counts both enslaved people and slaveowners among his ancestors, said that the church's delayed moral development on the issue of slavery constitutes "a wound in Christian memory, one from which we cannot consider ourselves detached."

"For this, in the name of the Church, I sincerely ask for pardon," he wrote.

Previous popes have addressed the church's legacy on slavery, but Leo's language appears to mark a development in how directly a pope links the church's moral failures to the institutional church itself, including the role of former popes.

In 1992, St. John Paul II had apologized for the role of Christians in slavery during speeches he gave in Cameroon and Senegal. He asked for pardon on behalf of "men belonging to Christian nations" and called for God's forgiveness for the sin of slavery "in which some baptized people took part without living out their faith," but he did not link the apologies as closely to the institution of the church. 

Magnifica Humanitas, however, raises questions over "exactly what space [Leo] is trying to lead us into by using the language much more of the church and the implication of his own predecessors' role [in slavery]," Rowlands said.  

"The context of these comments on slavery is looking also at modern slavery now, at contemporary slavery," she said. The pope is "saying we must not be in a position at some point in the future, [for] a successor of Pope Leo's, of having to make an apology" for "failing to recognize that there are new forms of slavery and subjugation, new colonialisms, that are connected with the AI and tech moment that we're in."

Leo says church's just war theory is 'outdated'

While Pope Francis questioned modern applications of the church's just war doctrine, Leo, reflecting on how technological developments shape humanity's practice and understanding of war, clearly affirmed that the church's teaching on just war must be reconsidered. 

Cardinal Michael Czerny, prefect of the Dicastery for the Promotion of Integral Human Development, said in response to reporters' questions on the church's just war teaching after the encyclical's presentation that "one cannot talk about just war." 

"There is the right to self-defense, but it is impossible to justify a war," he said. 

Leo did not propose an updated framework for understanding just war in his encyclical, but he wrote that "humanity possesses far more effective and capable tools for promoting human life and resolving conflicts, such as dialogue, diplomacy and forgiveness."

In a modern landscape which amplifies polarization through algorithms and makes war "culturally conditioned through simplistic narratives," Leo wrote that just war theory "which has all too often been used to justify any kind of war, is now outdated."

Rowlands said that Leo "doesn't completely repudiate" the church's teaching on just war in the encyclical, but rather questions the "the moral performance of just war theory," that is, using the church's just war framework to too easily justify conflict.

Modern technological developments, she added, puts just war theory "under increased moral pressure."

"That 'moral performance' question is placed under increased pressure when you look at what he talks about as the impersonalization of conflict and the rapidification of ways in which decisions are made."

Leo wrote at length in the encyclical about the dangers of entrusting lethal decisions in war to AI systems and warned that automation can create the false impression that human actors are less accountable for acts of war.

Just war theory made headlines within the church in the United States after Cardinal Robert McElroy of Washington stated that the U.S.-led war effort in Iran did not meet the moral criteria for a just war. 

Vice President JD Vance later publicly questioned the pope's understanding of the church's teaching on just war. 

In presenting his encyclical at the Vatican, Leo said that artificial intelligence is "dramatically changing how war is waged."

"Peace, not merely the absence of war, is justice at work," he said, "but when technology weakens our critical sense, peace itself is at risk."