Long time lurker, very rare poster, but your comment and the response really got my goat so to speak.
You could not be more wrong. The idea of “Just War” is neither a hallmark of Christianity or actually designed to prevent civilian casualties. Rather “Just War” is the logical outcome of the Whig/Marxist dialectic and by innate design, encourages totalizing wars of annihilation. The logic may seem counterfactual, but as with usual leftists plots, the path to hell is paved with good intentions.
Total war isn’t actually a modern concept, it is actually an ancient and primitive one. The complete destruction of an opposing group was the de-facto way of war since man was using wood clubs and flint spears. Even with the arrival of Christianity, this didn’t change much since the default method of warfare in Europe up into the late middle ages from the collapse of the Roman Empire was the Chevauchee, i.e. the civilian massacre.
The big break actually came following the bloodletting of the Thirty Years War and the new European balance of power that lasted up until the beginning of the 20th century. The general trend of European warfare from the late 17th century onwards were characterized by frequency but remarkably few casualties both military and civilian given the number of combatants involved. What generally happened was when once side was losing, they would surrender en mass or retreat and the other side would accept it and not murder all the captives as generally tended to happen before.
The reason why wars became less bloody at this time was not because of “Just War” but rather because war became legitimized for all parties involved. That is to say following Westphalia, notions of justice were simply irrelevant and wars became more like sporting contests. Sure you lost round one, but there is always next season and when all parties accepted the legitimacy of state aggression, the costs of losing wars became less onerous for the participants and thus the incentive to completely annihilate the others in an all or nothing gambit disappears.
“Just War” on the other hand returns us back to the earlier era where the legitimacy of all parties involved is not de facto acknowledged. Instead of recognizing winners and losers of political contests, it sees only the “Righteous” and the “Criminal”. Upholders of the so-called International Order and breakers of the Peace. Paradoxically, “Just War” theory rather than preventing conflicts which arises from differences in interests, serves to maximize grudges and encourage escalation. When all parties see one another as illegitimate enemies instead of competing principals, the stakes become all the higher and chancy wars of annihilation and the resultant civilian massacres become certain.