I am Catholic and I developed most of my Catholicism on studying the theological teachings of St. Thomas Aquinas and St. Augustine of Hippo. Two saints who contributed and influenced Just War Theory, the laws of war, and the moral philosophy of warfare. My Catholic Confirmation Saint is St. Michael the Archangel, the leader of the army of God. I also served 4 ½ years in the US Army Infantry as a Platoon Leader and Executive Officer. I found it critical, prior to me enlisting in the Army in 2013, to study and build a moral background so that I may perform my job to the best of my abilities. I have decided to share what I have learned throughout the years in a brief summary:
Just War Theory examines the moral justifications to go to war and to engage in war. Jus ad bellum and Jus in bello are the Latin translations for those theories. Jus ad bellum defines what justifies going to war while Jus in bello defines how combatants should behave while engaged in war.
Jus ad Bellum — Right to War
Jus ad bellum requires combatants to have a just reason to engage in warfare. Self-defense is a just reason. However, it would be unjust to engage in warfare to expand a colony and argue that your encroachment into other peoples’ lands is worthy of self-defense. It would be unjust to engage in war to defend stolen land or property. It would be just as unjust to engage in warfare to expel native populations from their land such as the idea of “Manifest Destiny”, where Americans justified the genocide of Native Americans and expelling them from their land as “God’s will.” Simply invoking a God does not justify immoral actions. God has been invoked to defend slavery and forced family separation before. We know what is right and what is wrong, God gave us a conscience. That is why we rush to defend and justify immoral actions. We know the action is wrong. Why else would we make up excuses? If it was a just action, you would need no excuse or justification.
The act of war an immoral behavior. Which is why you better have a damn good reason for it.
Jus in Bello — Right in War
There are two central principals, or pillars, in acting just while engaged in conflict. The principal of discrimination and the principal of proportionality. The principal of discrimination requires combatants to discriminate between combatants and non-combatants or civilians. It is unjust to blindly target civilians and civilian targets or to blindly engage randomly without clearly defining targets that are combatants. The principal of discrimination demands that to act justly in combat, you must target combatants and threats. Not hospitals, not news organizations, not schools, not culturally significant sites like Churches. You must target military targets, not civilians.
The principle of proportionality demands combatants engage in proportional levels of destruction that are related to a clearly defined objective. War will require combatants to destroy. Destroy lives, property, and kill other human beings. Therefore, that immoral behavior requires you do so proportionally. That you are only destroying and killing what is necessary. Not for fun, not for vengeance, not for retaliation, not for a message. Regarding the bigger picture, this requires combatants to engage using only necessary force to end the conflict as soon as possible. On the ground, combatants must engage in military actions that do not unnecessarily kill or destroy. This requires combatants to have discipline and sympathy to not engage in wanton or reckless destruction. If an enemy takes the lives of 10 of your civilians, it does not justify taking the lives of 100 of their civilians.
The Pragmatism of Just War Theory
Morality and winning are not mutually exclusive. In fact, morality can help you win. Morality can help you lead and recruit others who seek what is just. The distinct human advantage over other species of animals is our ability to cooperate and build. And we do so by being friendly, kind, and respectful of others. In Just War Theory, morality is an important tool. For Jus ad bellum, following the laws of war can help you avoid unnecessary combat that bleeds life, resources, and treasures. For Jus in bello, the principal of discrimination will guide you towards concentrating your firepower on necessary targets that are a threat. The principal of proportionality will preserve your resources in combat. Following the laws of war is not only moral it is efficient.