Throughout his papacy, Pope Francis was an outspoken critic of war and cautioned against abusing the “just war” theory detailed in the Catechism of the Catholic Church. As described in the just war doctrine of the Catechism, self-defense is only just “once all peace efforts have failed.” It also states that there are strict conditions for legitimate defense by military force that require “rigorous consideration.”

These factors, as outlined by the doctrine, include the damage inflicted by the aggressor being “lasting, grave, and certain”; all other means of ending the conflict must have proved ineffective, success is achievable, and “the use of arms must not produce evils and disorders graver than the
evil to be eliminated.”

In his 2020 encyclical “Fratelli Tutti: On Fraternity and Social Friendship,” Pope Francis wrote that in modern times “it is easy to fall into an overly broad interpretation of this potential right.”

“In this way,” Pope Francis continued, “some would also wrongly justify even ‘preventive’ attacks or acts of war that can hardly avoid entailing evils and disorders graver than the evil to be eliminated.”

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Soon after his papacy began in 2013, Pope Francis watched a full roster of conflicts unfold across the globe: Russia’s wresting control of the Crimean Peninsula in 2014; the rise of the Islamic State in 2015; Russia’s direct invasion of Ukraine in 2022; and the ongoing conflict between Israel and Palestine.

While acknowledging the right to self-defense, the Holy Father devoted most of his rhetoric to urgent pleas for avoiding war. “A war may be just. There is the right to defend oneself,” Pope Francis said in a June 2022 interview with Télam, Argentina’s national news agency. “But we need to rethink the way that the concept is used nowadays.”

In “Fratelli Tutti,” the Holy Father further noted the lurking threats of modern weapons of mass destruction. He wrote that humanity has never had “such power over itself, yet nothing ensures that it will be used wisely.”

“We can no longer think of war as a solution because its risks will probably always be greater than its supposed benefits,” Pope Francis added. “In view of this, it is very difficult nowadays to invoke the rational criteria elaborated in earlier centuries to speak of the possibility of a ‘just war.’ Never again war!”