In the months after Robert Prevost became Pope Leo XIV, in May 2025, he kept a relatively low profile. He fulfilled prescheduled trips to Turkey and Lebanon and released just one pontifical document, on the church’s love for the poor, begun by Pope Francis. But in 2026, Leo has come into his own with biblical messaging against war. At a Mass on January 1, after the Trump administration had killed more than 100 people by attacking boats in international waters in the preceding four months, the pope challenged policies undermining “diplomacy, mediation, and international law.” In an annual address to Vatican-accredited diplomats from 184 countries eight days later, he was even more pointed in his criticism: “War is back in vogue and a zeal for war is spreading.”

The Vatican’s criticism of militaristic policy caught the attention of the U.S. Department of Defense, which summoned the Holy See’s longtime nuncio (ambassador) to the Pentagon in late January. Tensions increased further in April, when American cardinals joined Leo in challenging the morality of war against Iran. Trump crudely assailed the pope on social media, denigrating him as “WEAK on Crime” and “terrible for Foreign Policy.” Vice President JD Vance piled on, attempting to lecture the pope on theology.

But the Trump administration’s attacks on the pope misunderstand not only the Catholic stand on war and the papacy’s opposition to what it sees as unjustified aggression. They also fail to comprehend that the pope, despite being American, is continuing to lead the Catholic Church away from the United States and Europe and toward a multilateral orientation. Unlike Francis, who was pigeonholed as anti-American in part because he was from Argentina and caricatured as overly preoccupied with the poor, Leo has garnered the broad support of U.S. and European bishops. Leo can carry on Francis’s vision of a more global—and more radically compassionate—church while criticizing U.S. foreign policy in a way his predecessor could not. An active American pontiff calling out U.S. actions in colloquial English gives the world an unexpected focal point for pushing back on Trump and forges more unity among American Catholics who were fiercely divided under Francis.

The pontiff’s frustration with the Trump administration’s foreign policy predates the U.S.-Israeli war on Iran. According to sources in the Vatican diplomatic corps, Leo took issue with Washington’s aggressive deportation of noncriminal immigrants, many of whom are Catholic; the 2025 U.S. national security strategy, which scorned multilateralism; and the military operation to seize Venezuelan President Nicolás Maduro and his wife and whisk them off to the United States. At the time of Maduro’s capture, Vatican officials were negotiating with the U.S. government to resettle the Venezuelan leader in Russia to avoid violence.

Trump’s first outburst against papal politics, in April, ultimately erupted after three U.S. cardinals appeared on the television show 60 Minutes and called the Iran war “unjust”—a theologically loaded word. But the president should not have been surprised by such criticism from the Vatican. The Catholic Church’s “just war” theory, rooted in ideas developed by the philosopher and theologian Saint Augustine, excuses war if it is necessary to restore peace and protect the innocent. War is morally acceptable only if it meets certain criteria. It must have a just cause—that is, to defend a jurisdiction against severe damage. It must be undertaken by a legitimate authority in the name of justice and peace and only as a last resort. And the actions of war must be proportional to the actions that caused it. Any violent engagement should not exceed the damage done by those who provoked it.

Popes have been........

© Foreign Affairs