Contra Pope Leo in “Magnifica Humanitas,” Just War Theory Is Not Outdated

In the few days since the issuing of Pope Leo XIV’s first encyclical, Magnifica Humanitas , many across the globe are responding to this 42,000-plus-word document, including technology leaders, investors, CEOs, theologians, lawyers, politicians, and more. While many Catholic voices have praised the encyclical for its guidance concerning artificial intelligence and the proper use of technology, other readers have found the encyclical more confounding than clarifying. I happen to be one of those.

Surely Leo is to be commended for attempting to contribute to Catholic social teaching, following in the footsteps of his namesake, Leo XIII, whose important 1891 encyclical Rerum novarum addressed “the social question” as it related to the industrial revolution. Fittingly, then, Leo XIV wishes to bring questions of human dignity, labor and capitalism, and the common good to bear on a topic of our day, AI.

In summary, the document seeks to apply the Church’s social teaching to AI by reconsidering the enduring questions of theological ethics for our technological age. AI must serve wider humanity rather than only the elite. While technology is not inherently evil, it is not morally neutral and hence must be “disarmed.” The document thus calls for stronger oversight, given what Leo believes to be its contribution to “worker displacement,” uneven wealth distribution, and significantly for readers of Providence , the “normalization of war” and “unending wars.” This emphasis on war and peace has been a regular fixture in Leo’s public pronouncements since his election to the papacy in May of last year. His back-and-forth disagreements with the Trump administration on war with Iran in recent months have been exceedingly public in nature, causing even Vice President Vance, a Catholic convert, to react.

At a recent Turning Point USA event at the University of Georgia, Vance, in a surprising degree of candor, responded to Leo’s earlier insistence that God rejects the prayers of “those who wage war” and that God is “never on the side of those who take up the sword.” Vance was moved to ask, on whose side was God when the Allies liberated France from Nazism and freed prisoners from concentration camps? Responding to the pope’s functional pacifism, the Vice President observed, “When the pope says that God is never on the side of those who wield the sword, there is a thousand-year—more than a thousand year—tradition of Just War Theory.” Vance concluded, “I think it’s very, very important for the pope to be careful when he talks about matters of theology.”

In a May 26 interview with NBC News, however, Vance offered praise for Leo’s AI warnings, calling them “very profound,” even when he conceded he has not read the entire encyclical.

It is not insignificant that one of the five chapters comprising Magnifica Humanitas is devoted to war. To be sure, the encyclical’s most important contribution is its reminder that technology is not morally neutral; moral truth must shape humanity’s design and use of technology, therewith contributing to the common social good. And indeed the words “common good” appear more often in the document (eighty-two times) than “artificial intelligence” (twenty-four times).

Fully aside from its length—245 paragraphs and 42,300 words—one is justified in questioning the overall coherence of the document. While Leo rehearses the development of the Church’s social doctrine with its undergirding principles—for example, human dignity, the common good, subsidiarity, and social justice (nos. 46-89)—as preparation for his main thesis, i.e., the dominance and dangers of AI (nos. 90-130), he injects other topics that appear unrelated. Among these are repeated, though vague, criticisms of “unemployment” (nos. 151-54, 166-67); his worry about the “climate crisis” and “climate change” as a “litmus test” for “social justice” (how this supposed “crisis” is a matter of “social justice” he does not say); the need to build a “civilization of love” (nos. 129-30, 182-87); and the Church’s past complicity in slavery and slave trade (no. 176). In a footnote, Leo identifies four papal bulls from the years 1435, 1442, 1452 and 1455 that are said to have expressly “relativized” the “problematic incompatibility of slavery with the Christian conscience” (n. 174). Not included in this list is one of his earlier namesakes, Pope Leo X, who in 1514 renewed the authority of earlier papal bulls that had granted Portuguese authorities the right to subjugate non-Christians and reduce them to slaves. This, in turn, would help lay the foundation for the transatlantic slave trade.

As it concerns the Church’s formal complicity regarding slavery, in the encyclical Leo confesses, “I sincerely ask for pardon” (no. 176). But if such confession, repentance, and need for pardon were a true and heavy burden that the Vatican actually carries, it would then seem appropriate that, at minimum, an entire encyclical in fact be devoted solely to the excruciating problem of the Church’s complicity in such evil. Perhaps such will be forthcoming.

As one European Catholic theologian observed, one might argue that Magnifica Humanitas is less a theological document than a political one. Indeed, the fact that (a) one-fifth of the document is devoted to issues of war and peace and (b) the document fails to interact with the theological and moral foundations of the just war tradition as taught by the Church—historically as well as in the Catholic Catechism— seems to confirm this criticism. Moreover, Leo’s authority is not in the area of artificial intelligence, which “goes beyond the philosophical strength of his arguments.”

With some justification, Father Gerald Murray, an expert in canon law and priest in the Archdiocese of New York, describes Magnifica Humanitas as “a tale of two encyclicals”: AI and war and peace. For Murray, the document advances a technocratic vision that encourages global governance (for example, by the United Nations, as stated in no. 226) and excessive regulation rather than offering true moral clarity in continuity with the Christian moral tradition as taught by the Church.

Indeed, there is verbal and situational irony in the fact that Leo, an Augustinian, has made it a central focus of his pontificate to continue the functional pacifism of his predecessor. In his 2020 encyclical Fratelli Tutti, Francis had warned, “War can easily be chosen by invoking all sorts of allegedly humanitarian, defensive or precautionary excuses, and even resorting to the manipulation of information. In recent decades, every single war has been ostensibly ‘justified.’” Thus, Francis concluded, “We can no longer think of war as a solution, because its risks will probably always be greater than its supposed benefits. In view of this, it is very difficult nowadays to invoke the rational criteria elaborated in earlier centuries to speak of the possibility of a ‘just war.’ Never again war!” In a footnote, Francis acknowledges that St. Augustine “forged a concept of ‘just war,’” but it is a concept that “we no longer uphold in our own day” (n. 242).

The change in the Church’s official teaching is made clear in Magnifica Humanitas : the concept of “just war” is “outdated,” Leo announces. Since his installation, of course, Leo has taken a strong stance against war, making numerous statements specifically critical of the war against the Iranian regime. Yet, pronouncements codified in an encyclical are different; they are considered authoritative. “Today, more than ever,” Leo declares, “it is important to reaffirm that the ‘just war’ theory, which has all too often been used to justify any kind of war, is now outdated” (no. 192).

One element in Leo’s argument is to decry the implications of AI in contributing to war. “No algorithm can make war morally acceptable”; that is, “moral judgment cannot be reduced to calculation.” Therefore, “it is not permissible to entrust lethal or otherwise irreversible decisions to artificial systems” (no. 198).

Part of Leo’s pacifist rationale follows: “The use of force, violence and weapons reflects a relational poverty that always has disastrous consequences for civilian populations” (no. 189). But this understanding of force does not align itself with the history of the Church’s thinking and teaching on “just war” and coercive intervention. Resort to arms is not only permissible, it is virtuous when and where motivated by “just cause” and “right intention.” The latter moral criterion was particularly important to St. Augustine, for whom charity and justice were wed. It is charity as well as justice, he believed, on at least three levels: to those who are committing evil, to those in society who are victims or who are watching, and to potential offenders who might be tempted toward evil in the future. Classic just war thinking understands war and coercive force as necessary for the express purpose of establishing a justly ordered peace. Its moral criteria apply to any age, even ours with its unprecedented technological developments.

Francis and Leo notwithstanding, the Church is not pacifist in her doctrine, as the nearly 2000-year-long conversation on justified use of force reminds us. The just war tradition extends from Augustine through Aquinas to early-modern theorists such as Francisco de Vitoria and Francisco Suárez into the present moment. It is only in the late twentieth century that the Church has become functionally pacifist.

The tradition of “just war” may be viewed as the chief moral grammar in our wider cultural heritage by which moral judgments concerning war and interventionary force should be shaped. For those of us who profess Christian faith, it is a method of moral reflection, and of statecraft, that refuses to separate theology and moral principle from politics. It presupposes not that war or coercive force can ever be perfectly “just”; only that in the temporal world, on this side of the eschaton, we must seek moral wisdom and discernment in arriving at judgments about war and peace.