A Fact Sheet on Just War Theory

Thoughts on applying the Christian tradition's guidelines for waging war

What is just war theory?
The Christian just war theory is a 1600-year-old attempt to answer the questions "When is it permissible to wage war" (jus in bello), and "What are the limitations on the ways we wage war?" (jus ad bellum).

Where did just war theory originate?
The first Christian thinker to write extensively about the subject was St. Augustine of Hippo. For Augustine, war was a logical extension of the act of governance. And governance itself was, as St. Paul wrote in Romans 13.1-7, ordained by God.

This, however, doesn't mean that all wars are morally justifiable. Augustine wrote, "It makes a great difference by which causes and under which authorities men undertake the wars that must be waged." This led him to describe the conditions under which war could be waged justly.

What does just war require?
For Augustine, the first requirement was proper authority. As he put it, "The natural order, which is suited to the peace of moral things, requires that the authority and deliberation for undertaking war be under the control of a leader." The leader Augustine had in mind was one whom God had entrusted with the responsibility of governance. In his time, this was the emperor. Later, it would be kings and princes. Today, it's our elected leadership. These people are answerable to God for the welfare of their states in a way that no private citizen is.Proper authority is not the only requirement. For Augustine, proper cause, the reasons for which we go to war, was as important as who authorized the action. He specifically ruled out as justifications for war such causes as "[t]he desire for harming, the cruelty of revenge, the restless and implacable mind, the savageness of revolting, [and] the lust for dominating." Augustine saw war as a tragic necessity and we should keep in mind his admonition to "[l]et necessity slay the warring foe, not your will."

Are there other requirements?
Augustine's ideas have been expanded upon over the years. In addition to proper authority and proper cause, Christian just war theory requires that there be a reasonable chance of success. Even if you have a good reason to attack, you cannot simply send young men out to die. Human life is too precious, too sacred to waste.

The final requirement is one of proportionality. In waging a war, authorities must make sure that the harm caused by their response to aggression does not exceed the harm caused by the aggression itself. Annihilating the enemy in response to an attack on one of your cities is an example of disproportion.

Similarly, proportionality has also come to mean that non-combatants must be shielded from harm. They can never, for any reason whatsoever, be the targets of an attack. The history of modern warfare is characterized by "total warfare," the expansion of targets beyond strictly military ones. That's why, of all the requirements of just war theory, proportionality is the most likely to be violated, even by governments with the most just of causes.