Pope Leo XIV Questions the Relevance of Just War Theory in the AI Era

Pope Leo XIV’s recent encyclical cautions that just war theory is often misapplied to endorse wars that should be condemned, and that the rapid evolution of weapons—including nuclear, cyber, drone and AI-driven systems—requires a fresh look at the doctrine’s safeguards. The piece reviews the historical development of the theory, beginning with Augustine’s insistence on legitimate authority, just cause and right intention, and Aquinas’s addition of proportionality and last resort.

Later scholars such as Vitoria and Grotius refined these ideas, and the Catholic Catechism now demands grave harm, exhausted peaceful options, reasonable chance of success, and avoidance of greater evils. While the author acknowledges the pope’s conclusion may be contested, he argues that misuse does not invalidate the framework, which should constrain rather than follow policy decisions. The article highlights U.S. constitutional war-power divisions and the law of armed conflict’s operational rules, using the Allied fight against Nazi Germany as a classic example of a just war. Finally, it warns that AI can improve precision but also risks moral abdication, urging that humans retain decisive authority over autonomous weapon systems, as reflected in DoD Directive 3000.09.