Pope Leo XIV questions Catholic just war theory in first encyclical

Pope Leo XIV’s first encyclical, Magnifica Humanitas, dated May 15, 2026, put Catholic just war theory under direct scrutiny, saying the tradition is “outdated” except in cases of “self-defense in the strictest sense.” The pope’s critique lands at a time of war in Ukraine and Gaza, along with fast-moving advances in artificial intelligence and military technology.

The 82-page document uses a broad reflection on AI to ask whether a framework associated with Augustine and Thomas Aquinas still fits modern conflict. In reporting on the encyclical, Leo warned that just war theory has “all too often been used to justify any kind of war,” a sharp rebuke to a tradition that was meant to restrain violence but has often been invoked to rationalize it.

The Vatican’s English text says the encyclical addresses war and peace, marriage and the family, economic and societal life, and the political community. That places the military discussion inside a wider statement of Catholic social doctrine, rather than treating armed conflict as a standalone issue. The same text presents the document as a major intervention on how Catholics should think about public life in an age of technological disruption.

The language is already prompting debate among Catholics and non-Catholics, with theologians and commentators reading it as an attempt to move the Church beyond a permissive reading of just war. That shift matters for Catholic politicians, diplomats and military leaders, who have long leaned on just war teaching as a moral test for the use of force. If Leo’s interpretation takes hold, it would tighten the conditions under which Catholics could defend military action in the language of conscience.

Magnifica Humanitas also includes an apology for the Catholic Church’s role in slavery, widening the encyclical’s moral reach beyond war. Taken together, the document suggests a pope willing to revisit more than one inherited Catholic judgment at once, from warfare to economic life to the Church’s own past. In a period defined by drones, autonomous systems and great-power rivalry, Leo is pressing the Church to decide whether an old vocabulary for limiting war has become a cover for it.