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The just war theory explained, in light of Iran war

March 17, 2026

My dear brothers and sisters in Christ,

Over the years I have written about the just war doctrine in light of various military conflicts that have arisen from time to time. Given that the United States and Israel are now at war with Iran, it would be good to review what the Catholic Church teaches about the just war doctrine.

St. Augustine (d. 430) was the original proponent of the just war theory, which St. Thomas Aquinas (d. 1274) later adapted and explained in his Summa Theologiae. The traditional elements of the just war theory are described in paragraph 2309 of the Catechism of the Catholic Church: The strict conditions for legitimate defense by military force require rigorous consideration. The gravity of such a decision makes it subject to rigorous conditions of moral legitimacy. At one and the same time: 

  • The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain; 
  • All other means of putting an end to it must have been shown to be impractical or ineffective; 
  • There must be serious prospects of success; 
  • The use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modem means of destruction weighs very heavily in evaluating this condition. … 
  • The evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good. 

It will also be helpful to recall the words of the Catholic Bishops of the United States in their 1983 pastoral letter on war and peace entitled, The Challenge of Peace: God’s Promise and Our Response. The writing of the pastoral letter was entrusted to a committee headed by Cincinnati Archbishop Joseph Bernardin, who would soon thereafter be named the new Archbishop of Chicago and elevated to the College of Cardinals by Pope John Paul II. 

In The Challenge of Peace, the bishops said that “Catholic teaching begins in every case with a presumption against war and for peaceful settlement of disputes. In exceptional cases, determined by the moral principles of the just-war tradition, some uses of force are permitted.” The Challenge of Peace affirms, “Every nation has a right and duty to defend itself against unjust aggression,” however, “Offensive war of any kind is not morally justifiable.”

In addressing issues of war and peace, bishops “speak as pastors, not politicians. We are teachers, not technicians. We cannot avoid our responsibility to lift up the moral dimensions of the choices before our world and nation.”

What about the teaching of Jesus in His Sermon on the Mount, in which He taught, “You have heard that it was said, ‘An eye for an eye and a tooth for a tooth.’ But I say to you, offer no resistance to one who is evil. When someone strikes you on your right cheek, turn the other one to him as well” (Matthew 5:38-39). The New Jerome Biblical Commentary says that Jesus offers this teaching as “a strategy for winning, not for passive resignation or indifference to evil. The goal is to shame the opponent into a change of heart. This presupposes the requisite dispositions in the opponent, which are not always present.”

Self-defense does not require waiting for the aggressor to fire the first shot. If the threat is imminent, steps may be taken to thwart the attack. While the extent of Iran’s military capabilities and their intentions to use their weapons to attack the United States and Israel is not publicly known, our political and military leaders must rely on the intelligence and assessment of the threat as available to them.

Efforts to dialogue and negotiate with the Iranian regime appear to have been futile. Similarly, efforts to appease the rulers of Iran with financial inducements have not borne fruit. 

Neville Chamberlain, who served as British Prime Minister from May 1937 to May 1940, was one of the chief proponents of appeasement towards Adolf Hitler prior to World War II. Chamberlain and Hitler signed a document at the Munich Conference of 1938 promising that Britain and Germany would promote peace in Europe. Chamberlain returned to London and announced that he had secured “peace in our time.”

Winston Churchill, who succeeded Chamberlain as British prime minister in 1940, was a fierce opponent of appeasement. He said, “An appeaser is one who feeds a crocodile, hoping it will eat him last.” Churchill was convinced that Hitler would not stop, and of course, we know now that he was right. Hitler did not stop until he was defeated. Many people fear the same with Iran.

In the end, decisions about war and peace are made by governmental and military leaders, but their decisions must be informed by moral principles that weigh the pros and cons of military engagement in accord with the just war tradition. Such decisions must also be guided by prayer, remembering the call of Jesus to be peacemakers in our own time and situation.

May God give us this grace. Amen.