VATICAN CITY – In a significant theological shift, Pope Leo has formally rejected a foundational Catholic teaching that has guided church thinking on warfare for more than 1,500 years, according to a new papal document released this week.
The pontiff’s abandonment of the ‘just war’ doctrine came in his inaugural major encyclical published Monday, which also called for worldwide oversight of artificial intelligence systems and delivered the church’s most direct acknowledgment of its historical involvement in the Atlantic slave trade.
“The ‘just war’ theory which has all too often been used to justify any kind of war, is now outdated,” Pope Leo stated in the document titled “Magnifica Humanitas” (Magnificent Humanity).
“Humanity possesses far more effective and capable tools for promoting human life and resolving conflicts, such as dialogue, diplomacy and forgiveness,” the pope wrote.
Chicago Cardinal Blase Cupich, a papal confidant who attended Monday’s Vatican unveiling, explained to Reuters that the pontiff worries about world leaders misappropriating the doctrine to validate military actions.
“We have to make clear that the just war theory was always meant to be a restraint, not a permission slip which sadly some are misusing to justify their decisions to go to war rather than seek the ways of peace,” Cupich stated.
The papal declaration comes amid tensions with the Trump administration, particularly after Pope Leo criticized the Iran conflict. The pontiff has recently adopted stronger language and drawn criticism from President Donald Trump.
Trump administration figures, including Catholic Vice President JD Vance, have referenced the just war principles to defend the Iran military campaign. Following an April social media post from the pope’s account stating God “is never on the side of those who once wielded the sword,” Vance responded at a Georgia gathering, suggesting the pontiff should “be careful when he talks about matters of theology.”
British scholar Anna Rowlands, who participated in Monday’s Vatican presentation, told Reuters that Pope Leo is addressing concerns about “a new age of changing conflict, now increasingly tech driven.”
“It is a strong statement about the need for (just war theory) to be placed in a renewed wider context of criteria for building peace and resolving conflict,” Rowlands said regarding the pope’s outdated theory declaration.
The warfare doctrine traces back to St. Augustine of Hippo, an influential early church leader who inspired Pope Leo’s priestly vocation. The pontiff belongs to the Augustinian religious community based on the saint’s principles.
Augustine, who passed away in 430 AD, established specific standards for determining legitimate warfare. He argued conflicts should aim only to restore peace and never stem from cruel motivations.
These Augustinian guidelines continue as fundamental curriculum at global military institutions, including West Point, the Naval Academy, and Air Force Academy in America.
Some Iran war opponents have also cited Augustine’s framework to challenge the conflict, which began with coordinated U.S.-Israeli surprise attacks on Iran February 28. Washington Cardinal Robert McElroy declared the war “morally illegitimate” in April, referencing Augustine’s teachings.
Marie Dennis, former head of the global Catholic peace organization Pax Christi, said Pope Leo’s document “exposes the fiction of a ‘just war’ with the truth about a culture of power that is normalizing war.”
“Pope Leo joins millions of others around the world, including in the U.S., who see hope in the proven effectiveness of nonviolent strategies for protecting democracy, transforming conflict, and legitimate defense,” Dennis concluded.
