During Lent this year—while the church was calling on American Catholics to pray, fast and give alms—the United States government spent $2 billion dollars a day carpet-bombing Iran, assassinating its leaders and killing thousands of its citizens, including hundreds of women and children. The gash of war amid the holiest days of the Christian calendar also exposed new divisions between President Donald Trump’s MAGA coalition and the spiritual authority of the Vatican. If his predecessors were slow to denounce the First and Second World Wars, Pope Leo XIV seems determined not to repeat their mistakes as the United States appears ever less cautious about setting off the third.

After coming to power in part by promising to end America’s “forever wars,” President Trump vowed that “all hell” would rain down on Iran and shocked the world with genocidal threats. Defense Secretary Pete Hegseth asked Americans to pray “every day, on bended knee” for a military triumph “in the name of Jesus Christ.” 

Yet over the same weeks, Pope Leo has made strong statements condemning all wars. In his Palm Sunday homily, he announced that Jesus is the “King of Peace, who rejects war, whom no one can use to justify war” since “he does not listen to the prayers of those who wage war, but rejects them.” In Cameroon this month, Leo said: “Blessed are the peacemakers! But woe to those who manipulate religion and the very name of God for their own military, economic and political gain, dragging that which is sacred into darkness and filth.” 

According to supporters of President Trump, Pope Leo is guilty of “overstatement” for expressing Catholic social teaching in terms that teeter on the edge of pacifism. Speaker Mike Johnson echoed the sentiments of many Republicans when he said on Capitol Hill he “was taken a little aback” by Pope Leo’s admonishment since “there’s something called the just war doctrine.”

Despite clear and public teaching by U.S. bishops and cardinals, some American Catholics might wonder how just war theory applies to wars spanning the globe today. To understand Pope Leo at this moment, we can turn to the wisdom of St. Augustine of Hippo, the great doctor of the church who is the namesake of the pope’s Augustinian order. 

This is not the first time that Augustine’s theology has risen to the surface of American politics. When President Joe Biden invoked Augustine’s The City of God (Book XIX.24) in his 2021 inaugural address, First Things called it a “misreading.” Last year, Vice President JD Vance, a Catholic convert who has shared more than one opinion at odds with Catholic doctrine, claimed that Augustine’s ordo amoris in Book XV.22 justified Christian nationalist support for favoring more proximate neighbors over immigrants. Pope Francis informed the U.S. bishops that Vance was incorrect. Last week, Mr. Vance said at the University of Georgia that the pope was wrong to teach that Christ is “never on the side of those who once wielded the sword and today drop bombs.” “I think it’s very, very important for the pope to be careful when he talks about matters of theology,” Mr. Vance said, claiming that the “thousand-year tradition of just war theory in Christianity” was on his side. 

Regardless of the outcome of any tensions between the Vatican and Washington D.C., what the vice president and other critics of Pope Leo forget is that the priority of peace fundamentally grounds Augustine’s just war theory. Pacifism is not incidental but essential to it. 

Augustine’s theory holds together the seeming opposition between the passive suffering of Jesus at the hands of the Roman Empire and the biblical tradition of soldiers fighting with God’s support. His heterodox opponents, like the Manichaean bishop Faustus, held that examples of religious warfare in the Old Testament contradicted Jesus’ teachings to turn the other cheek and “offer no resistance to one who is evil” (Mt 5:39)—not to mention the heroic pacifism of early Christian martyrs. For Augustine, this would mean that “Christ abolished” the Old Testament “by enjoining the opposite” when it came to mercy, chastity, poverty and warfare, which is absurd. 

Rather, Augustine explained, peace paradoxically perfects warfare, just as chastity perfects erotic love, mercy perfects justice and voluntary poverty perfects the blessings of wealth. So too, the pacifist martyr is the greatest soldier whose loss wins the greatest battle. Augustine writes that the witness of the martyrs reveals “another life for which this life ought to be disregarded, and another kingdom for which the opposition to all earthly kingdoms should be patiently borne.”

Augustine was horrified by war. As he repeats throughout Book XIX of The City of God, war is one of the chief sources of human suffering. “The human race is made even more miserable,” he writes, “either by warfare itself, waged for the sake of eventual peace, or by the constant fear that conflict will begin again.” Even a just war is a time of “misery,” waged with tremendous regret and mourning. To bring an end to greater violence, Christians sometimes, as if through tears, must “make use of the peace of Babylon.” But such wars are an absolute last resort, not begun on impulse, animated by the thrill of weaponry or the bloated cravings of domination. Augustine’s words are worth quoting in full in 2026: 

Let everyone, therefore, who reflects with pain on such great evils, upon such horror and cruelty, acknowledge that this is misery. And if anyone either endures them or thinks of them without anguish of soul, his condition is still more miserable: for he thinks himself happy only because he has lost all human feeling.

Writing against Faustus, Augustine insisted that “the real evils in war are love of violence, vengeful cruelty, fierce and implacable enmity, wild resistance, and the lust of power.” This means that even if “good men undertake wars,” still “a great deal depends on the causes for which men undertake wars.” In the midst of warfare, Christians should be imbued with peace in their “inward disposition” lest they begin to love violence, celebrate cruelty and relish hegemony. 

As Augustine wrote in Letter 189, “peace should be the object of your desire…[and] even in waging war cherish the spirit of a peacemaker.” That is, a just war is fought for the sake of peaceful reconciliation with the opponent. The just warrior will even endure some harm rather than injure the innocent. Peace is the goal, and peace is part of the means. In this way, pacifism perfects just warfare by both promoting the common good and constraining excess violence.

There is something otherworldly, one might even say “utopian,” about Augustine’s conception of warfare. He never lets go of the moral priority of peace; he never fails to demand that human cities come to imitate the perfect peace of the city of God. In this regard, it is nearly impossible to exaggerate or “overstate” the importance of peace in Augustine’s just war theory. As Pope Leo recently posted on X, echoing Augustine’s thought, “let us reject the logic of violence and war, and embrace peace.”

When Pope Leo teaches the absolute priority of peace, he is not somehow oblivious or ignorant of just war theory. Rather, he is calling us to ask: Why have so many American Catholics forgotten their tradition’s radical insistence, for over a millennium, on striving for peace at all costs, hungering for peace, even suffering for peace, imitating the pacifism of the martyrs? 

Misunderstandings of Augustine have long accompanied the rise of the United States as a global nuclear superpower. Protestant theologians like Reinhold Niebuhr—on the cover of Time magazine in 1948—offered a way for Christians to assuage their uneasy consciences. Niebuhr’s “Christian realism” claimed that while we await the coming city of God, American power could be exercised vigorously—ruthlessly if necessary—in this fallen world given over to the cities of men. It was a matter of prudence, in this view, not to fall sway to naïve pacifism. 

Armed with this sharp division between public realpolitik and private Christian morality, Protestant and Catholic leaders could now countenance the American empire. Recently, scholars have shown that Niebuhr seriously misread Augustine.

The spectacular irony of our moment is that in opposition to the first American pope, some of the most vocal Catholic leaders in the United States are promoting Niebuhr’s theory of war. Chief among these is Mr. Vance, who told Pope Leo to “stick to matters of morality” and allow President Trump to “dictate” public policy. But it is likewise a view held in various forms by countless rank-and-file American Catholics seeking to negotiate the discomfort of the worldwide military dominance of the United States and Catholicism’s rival claims to global authority. 

Yet no Pax Americana—however tempting to many—should be confused with the peace of Christ’s church. Alas, this impulse—to insulate American foreign policy from Catholic social teaching—heralds a return of Niebuhrian Christian realism and all of its compromises and confusions. We can be grateful that a true Augustinian sits in the chair of Peter.

Jason Blakely is starting this fall as professor of philosophy at Loyola Marymount University in Los Angeles. His book Utopia for Our Century: A Manifesto of Hope, coauthored with David Albertson, is out July 21 with Yale University Press.

David Albertson is professor of religion and philosophy at the University of Southern California. His book Utopia for Our Century: A Manifesto of Hope, coauthored with Jason Blakely, is out July 21 with Yale University Press