That great church father and “just war” theorist, Augustine of Hippo, had this to say (among other things) in justifying war:
“What is the evil in war? Is it the death of some who will soon die in any case, that others may live in peaceful subjection? This is mere cowardly dislike, not any religious feeling. The real evils in war are love of violence, revengeful cruelty, fierce and implacable enmity, wild rebelliousness, and the lust of power, and such like; and it is generally to punish these things, when force is required to inflict the punishment, that, in obedience to God or some lawful authority, good men undertake wars” (Contra Faustum 22).
There are three points I would like to deal with here that Augustine makes:
1. War is excusable because the person you kill will die soon anyway, and fighting wars will bring a peaceful society.
2. The real evil in war is not killing, but the hateful attitude.
3. Going to war is done in obedience to God or a lawful authority instituted by God.
What about this argument that war is not actually evil since it only destroys a life which is destined to be taken regardless? Let’s take another kind of killing that many Christians agree qualifies as a moral evil–abortion. Is abortion not simply the taking of a life which will be lost some day anyway? Indeed can abortion be an evil in itself since most women don’t destroy their babies out of a “love of violence,” but to achieve a higher and better end–namely, that they may “live [more peacefully]” after the deed has been done? Killing a child who can’t be fully supported, or who will get in the way of the mother having a fulfilled and peaceful life, couldn’t be wrong, could it? It seems then that while motivation may play a part in our defense before the divine judge, it does not make any of our actions actually good in and of themselves so that we can justify undertaking them in the future.
Unlike many modern Christians who justify war but cannot justify abortion, the early church saw them as clear parallels:
“And when we say that those women who use drugs to bring on abortion commit murder, and will have to give an account to God for the abortion, on what principle should we commit murder? For it does not belong to the same person to regard the very fœtus in the womb as a created being, and therefore an object of God’s care, and when it has passed into life, to kill it…” (Athenagoras, 177 A.D. A Plea for the Christians, chapter 35).
As for Augustine’s third point, isn’t he using circular reasoning? Whether or not war is obeying God or “lawful authority” is precisely what is under debate. If disciples of Christ are forbidden to fight in wars, then by definition going to war is disobedience to God.