Pope Leo XIV to Reconsider Just War Doctrine Amid Tensions with US Administration

ROME — In a move likely to further raise tensions with the administration of U.S. President Donald Trump, Pope Leo XIV will gather the world’s cardinals behind closed doors on Friday to hash out new guidelines on when war is justified.

It’s a topic that has already fired a spat between the White House and the Vatican within the context of the Iran conflict.

When Leo said the disciples of Christ were never on the side of those who “once wielded the sword and today drop bombs,” Vice President JD Vance retorted that the pontiff needed to be “careful” about his theology, given the Church’s long-established theory of a just war.

Rather than simply being “careful” about a centuries-old doctrine of just war — dating back to St. Augustine in the 5th century and St. Thomas Aquinas in the 13th century — Leo reckons the Church should be reconsidering whether this traditional framework still holds in an age of drones, cyber-warfare and nuclear weapons.

In an assertive papal document last month, known as an encyclical, Leo said the theory, “which has all too often been used to justify any kind of war, is now outdated.” Days later, he told journalists, “The notion of a just war no longer applies … [The theory] was developed in centuries when no one could have imagined the weapons we have today or humanity’s capacity for destruction.”

Senior clergy expected that the gathering of cardinals could move toward stricter definitions of when war is justified in self-defense — particularly relevant in relation to Iran — and impose greater demands for negotiation before potential conflicts.

Archbishop Timothy Broglio, head of the U.S. Archdiocese for the Military Services, who has argued that the U.S. war with Iran does not meet the conditions for a just war, said the changing nature of warfare demanded a fresh examination of the doctrine.

“Because of the cataclysmic encounters that we’ve had and also the potential danger that’s there, I think the pope wants to take advantage of bringing to bear all of the modern considerations that now have, in a very real way, altered the nature of warfare,” Broglio said.

Monsignor Vincenzo Paglia, president emeritus of the Pontifical Academy for Life and one of the Catholic Church’s most prominent peace negotiators, said Leo was “stepping on the gas” of a process begun by previous popes, describing it as “Leo’s first big move.”

Pope Benedict XVI reaffirmed the duty of self-defense, while Pope Francis increasingly questioned whether modern warfare could still satisfy the traditional criteria of a just war.

“I believe the popes are advancing the theological doctrine of peace,” Paglia said. “The Church isn’t a museum. It’s a living body.”

The extraordinary consistory of cardinals on Friday gives Leo the opportunity to do more than restate his own position or issue another appeal for peace. Rather, it allows him to marshal the collective authority of the College of Cardinals behind his position and transform what has so far been his own teaching into the emerging consensus of the Church, analysts said.

Francesco Sisci, director of the Rome-based Appia Institute think tank, said any statement emerging from the meeting “would have greater force.”

While Sisci expects broad agreement among the cardinals, he said a small minority of clergy continued to provide theological cover for supporters of the war.

“It’s messy,” he said. “If JD Vance and [tech billionaire] Peter Thiel are claiming Iran is a just war, maybe it’s because there are priests who are lending them credence.”

While some Catholic peace activists have called for the total abandonment of just war doctrine, senior clergy say Leo’s ultimate aim may be to narrow its application so that only the strictest cases of self-defense could satisfy its moral requirements.

Broglio suggested it could evolve to distinguish more clearly between wars of defense and preventive military action.

“I would see the situation in a place like Ukraine that was attacked as being much different from the preventative approach to some place like Iran,” he said.

The global composition of the group, including bishops from regions that have experienced chronic violence, might introduce nuances that would enrich the discussion, Broglio said.

He expected the meeting’s most immediate message to be less about rewriting theology than changing the way governments approach conflict.

“The message that comes out of the consistory could be an appeal to negotiate before, not after, a conflict,” Broglio said.