Pope Leo XIII updates just war theory

Pope Leo XIII has begun updating the Catholic Church’s “just war” theory for the first time in a century, signaling a shift away from traditional military doctrine toward a stronger emphasis on diplomacy and peacebuilding. The Vatican confirmed the review on Tuesday, framing it as part of the Church’s ongoing response to modern conflicts, including Russia’s war in Ukraine and rising global instability. The move reflects growing concerns among Catholic leaders that old frameworks no longer address today’s wars, which increasingly target civilians and involve cyberattacks and nuclear threats.

The “just war” theory, developed over centuries, has long justified warfare under strict moral conditions—such as self-defense and proportionality. But critics, including many within the Church, argue the theory has been used to rationalize violence rather than prevent it. Pope Francis has already distanced himself from the concept, calling war “a defeat for humanity.” The update comes as younger Catholics, especially in the Global South, increasingly reject traditional justifications for violence. The review is expected to prioritize nonviolent conflict resolution, economic sanctions, and humanitarian intervention over military action.

This shift has been building for years. Pope Benedict XVI quietly questioned the just war framework in 2009, and Pope Francis has repeatedly condemned nuclear weapons and arms races. The Vatican’s Dicastery for Promoting Integral Human Development is leading the effort, consulting theologians, military ethicists, and peace organizations. A draft of the updated teaching could be released as early as next year, potentially influencing Catholic politicians and military leaders worldwide.

If adopted, the new doctrine could reshape global ethics around war. It would align the Church more closely with pacifist movements while challenging nations that claim religious backing for their military campaigns. The update also matters for millions of Catholics who look to the Pope for moral guidance on issues like drone strikes, cyber warfare, and climate-related conflicts. A modernized just war theory could finally move the Church—and the world—away from the idea that war is ever truly “just.”