Taken from Kingdom Ethics by Glen Stassen and David Gushee, InterVarsity Press, 2003.   Available on Amazon and elsewhere.

In the 4th Century, Emperor Augustine of the Christian Roman Empire postulated a “Just War Theory,” which Thomas Aquinas, whom the Catholic church considers one of its greatest theologians, codified in the mid-1200s, and which has remained the basis for the theory these past 800 years. Please note, this is not a theory to justify a war, but if a war is to be fought, this is how it should be done.  

The Just War Theory was an important part of a sermon I presented on the 100th Anniversary of Armistice Day on November 11, 2018. You can find that sermon at

From Kingdom Ethics:
The Just War Theory makes the logical point that in order to justify the killing that occurs in war, there must be a reason so important that it overrides the truth that killing people is wrong.

The moral theory of the Just War “begins with the presumption which binds all Christians: we should do no harm to our neighbors; how we treat our enemy is the key test of whether we love our neighbor; and the possibility of taking even one human life is a prospect we should consider in fear and trembling.”

The reasons come in the form of criteria for when a war is just. All Christians – and others – need to know and remember the eight criteria of Just War Theory. Only if we know the rules that determine when war is just or unjust can we exercise our conscientious responsibility in deciding whether to support or oppose a ware which a government proposes to wage on our behalf.

1. Just Cause. This includes the stopping of a massacre of large numbers of people and stopping the systematic and long-term violation of the human rights of life, liberty and community.

Some say that only the defense of one country from attack by another counts as just cause for war.

Some add the criterion that the side wagering a “just war” must have a comparatively more just cause than the other side, but most everyone thinks their own cause is more just than the other side’s. Therefore we stay with the more objective definition (listed above).

2. Just Authority. Constitutional processes must be followed, so the people who will pay with their lives and resources will be represented in the decision. Furthermore, the approval of the United Nations or a representative international body or coalition should generally be sought.
For these two kinds of just authority to function, both government truthfulness and freedom of the press are required so that people can judge situations accurately. Deceitful authority is unjust authority, especially when the deceit is in the service of getting people killed.

3. Last Resort. All means of negotiation, conflict resolution and prevention must be exhausted before resorting to war.

4. Just Intention (Final Cause or Future Aim). “The only legitimate intention is to secure a just peace for all involved. Neither revenge nor conquest nor economic gain nor ideological supremacy are justified.”

5. Probability of Success. “It is wrong to enter into a war that will kill many people … in order to achieve a more important goal, if we will quite surely lose and not achieve that goal, and all those people will die in vain.”

6. Proportionality of Cost. “Proportionality requires that the total good achieved by a victory will…outweigh the total evil and suffering that the war will cause. No one should prescribe a cure that is worse than the disease.”

7. Clear Announcement. The government that is about to make war must announce its intention to make war and the conditions for avoiding it. Stipulating the conditions for avoiding war enables the other side to know what it would take to avoid or stop the war.

8. The War Must be Fought by Just Means. (U)sing the huge arsenals of nuclear weapons would cause far worse destruction than any alleged gain, and so any nuclear war would be unjust.
Forbid(den) is “direct, intentional attacks on nonmilitary persons (and) individuals not actively contributing to the conflict.” Bombing a military target like a tank or a weapons factory may have the indirect effect of killing some civilians. That is a realistic and allowable consequence of war (though nonetheless horrible), so long as it truly is unintentional and indirect, and its cost in lives is proportional to the gain.


Use of Just War Theory must be based on nonviolence and justice. A Christian who supports Just War Theory should see it as the most effective way to minimize violence and injustice, not merely to rationalize making war. “Just War Theory does not try to justify war. Rather it tries to bring war under the control of justice.”