Defining the Justice of a Just War

May 26, 2023 | Articles, Living in the World, Suffering with Christ

By Vir Christi

War has always been a tragic part of the human condition.  Talk about what constitutes the circumstances for a “just war” has dominated philosophical circles since the earliest centuries of the Catholic Church, and continues even to this day.  How do we, as Catholics, discuss war when people bring it up around holidays like Memorial Day?  

Fortunately, the Church articulates it clearly for us!  She divides it into three categories: just cause, justice in war itself, and just peace.

Just Cause (Ius ad Bello)

St. Thomas describes three conditions that are necessary for a war to be defined as “just”: one, it must be conducted by lawful authority; two, the cause for which the war is fought must be just; and three, that the intention of those entering into the war should be to advance a righteous cause.  Philosophers coming after Saint Thomas have added the war must be an absolute last resort, have a reasonable chance of success, and the end is proportional to the means that are being used.

Taking all of the above together, this means that a just war has clearly defined aims for the purpose of redressing some wrong or bringing about some good.  All other means of  conflict resolution short of war must be exhausted before war can be initiated, since the inherent nature of war is unjust to both combatants and noncombatants alike.  Certainly, all of that seems self-explanatory.  The part where many people struggle comes with the dimension regarding the “reasonable chance of success.”

Despite the aversion to religion in recent generations, our society loves the idea of the fallen martyr in a hopeless cause.  The popularity of movies like Braveheart and Lord of the Rings, which frequently describe the “good guys” being hopelessly outnumbered without a chance of victory, has driven home a desire in the hearts of many people to fight even when victory is not readily apparent.  Uncomfortable as it is to admit, this idea flies directly in the face of what it means to wage just war.  The aim of a just war is to redress the wrong that has been done as quickly as possible, with minimal loss of life and the least damage to property.  To go to war in a hopeless cause increases property damage and the potential for loss of life, without a meaningful solution being rendered as the trade-off.

Once the just cause has been established and war has begun, focus turns to conduct during the war.

Just Conduct (Ius in Bello)

More than a just cause or a just peace, this category received the greatest amount of scrutiny in the second half of the twentieth century and continues to be scrutinized into the twenty-first century.  Contemporary examinations of how wars like the Second World War were waged have revealed that both sides in many modern wars have been guilty of the callous loss of life.  People decry the Germans for their relentless bombing of London during the Second World War, but the Allies fire-bombed Dresden and Tokyo and other targets that carried no real military significance to the war effort of the Axis.  So how do we determine just conduct in war?

Waging a just war is more difficult in our time than in the time of St.Thomas, because the way wars have been fought has changed.  In medieval times, armies would ride to distant battlefields and fight; victory in war was declared when one army destroyed the other, or if a monarch fell on the battlefield.  Civilians were rarely involved because of how clearly battles were separated from the populace outside of siege warfare.  Beginning with the Vietnam War, a new problem was highlighted in modern warfare: what to do when enemy combatants are willingly hiding among the civilian populace, or when the civilians themselves have taken up arms against the occupying army?

There are three core principles to just conduct in war: first, avoiding the intentional killing of non-combatants; second, acting proportionally towards the objective one desires to complete; and third, holding the agents of war responsible for their actions.  Accidentally killing civilians, such as in an airstrike aimed at what is believed to be an enemy’s forward defensive position but which is actually a civilian air raid shelter, is not a violation of just war theory.  Proportional response towards an objective would be something like what the coalition did in the First Gulf War to expel the Iraqi armies from Kuwait, but then ceasing their advance once Kuwaiti sovereignty had been re-established.  Finally, holding agents responsible means that while soldiers might not be responsible for starting a war, they can—and should— be held accountable for immoral actions they willingly undertake during war.  This means that “just following orders” is not a moral license to commit unethical acts.

Just Aftermath (Ius post Bellum)

Establishing a just peace can be as difficult as behaving justly on the road to war and in conduct during wartime.  The goals of a just peace are aimed at considering the culture and customs of the defeated, proportional to the type of victory won (was the enemy completely defeated or was a cease-fire declared?), claims for compensation should be fair and within the means of the defeated, and separating aggressors from non-aggressors.  Furthermore, ideally, a just peace will seek to bring the defeated aggressor back into the fold of people/nations.

Bringing about such a peace is a difficult thing under the best of circumstances, and the aftermath of a war is far from that.  Think about the victorious Allies at the end of the First World War: they had not militarily defeated Germany as much as fought the German armies to an exhausted standstill.  The Germans would have been overcome after another year or two of bloody combat, but the loss of life to achieve that outright victory would have been staggering. The Germans chose not to engage in futile resistance to save lives, and the Allies could have responded generously to the gesture.  Instead, the Allies acted as though they had crushed Germany with overwhelming force and treated the Germans contemptuously; this sowed the seeds for a second and far bloodier conflict twenty years later.

A just peace requires tempering one’s emotions in the aftermath of victory, both joy at having won the war and bitterness or anger towards one’s enemies for hardships caused during the war.  It recognizes that the long-term goal of maintaining peace is still a valuable one, even if it failed in the interim, and seeks only to correct injustice. It goes no further and seeks nothing in the way of retribution or punishment.

What Does This Mean for Our Time?

In the modern era, where societies have wholesale lost an appreciation for the intrinsic value of the human person (look no further than the conversation on abortion), this is more relevant than ever.  People are already at risk of dehumanizing those who do not share common beliefs with them.  It is not a stretch to imagine that if it came to war, such dehumanization could be applied with horrifying ramifications on the battlefield or in establishing a postwar settlement.

Now more than ever, talking about what makes a just war is important.  We have to keep talking about it, because if we do not, those small arguments that cloud people’s ability to see the other person as they are can gather into something far darker.  And as Our Lord gently reminds us, “Whoever is dishonest in a very little is dishonest also in much.” (Luke 16:10)  We can respect the sacrifices our military personnel make this Memorial Day, while also remembering that we want them fighting for the just causes.

Further Resources on Just War:

Vir Christi

Vir Christi

Vir’s heart has been on fire for the Church from day one, and he dreams of the day when Constantinople will be a city again. He has a competitive drive satiated by sports and board games, but is also just as happy to sit down and read a good book for hours on end.


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