What did Christians think about war?

Celsus had urged Christians to fight for the emperor and, if he required it, to serve under him. Origen answers directly: "none fight better for the king than we do. We do not indeed fight under him, although he require it; but we fight on his behalf, forming a special army", which he calls "an army of piety", "by offering our prayers to God."

He argues it by analogy with pagan priests, who were exempted from the army so their hands stayed clean for sacrifice. The refusal is presented as a recognised category rather than as sedition, which is how you argue when you are a minority explaining yourself to a hostile majority.

Tertullian, on a soldier who refused a garland: "I think we must first inquire whether warfare is proper at all for Christians." His reasons are the military oath alongside the oath to Christ, and the sentence about him who uses the sword perishing by it.

The objection is not only to killing. It is to the oath, the guard duty at temples, and the punishments a soldier administers: a whole occupation, not a single act.

He was arguing with other Christians as much as with Rome. The soldier had stood out "among so many soldier-brethren", and Tertullian writes to refute "the laurel-crowned Christians themselves".

Romans has the authority as "a servant of God, an avenger for wrath to him who does evil", who "doesn’t bear the sword in vain", and tells every soul to be in subjection to it.

A tradition holding both that and the instruction to love enemies has a problem to solve rather than a rule to apply, and it solved it differently before and after it acquired an empire.

Augustine, writing to a Roman officer: "peace should be the object of your desire; war should be waged only as a necessity, and waged only that God may by it deliver men from the necessity and preserve them in peace", and "peace is not sought in order to the kindling of war, but war is waged in order that peace may be obtained."

This belongs to the beginning of a doctrine rather than a permission slip: it sets conditions, and conditions can be failed. It is also unmistakably advice to a man with an army, which the earlier writers were not in a position to give.

The writers who condemn military service are evidence that Christians were in the army, or there would be nothing to condemn. Tertullian himself boasts elsewhere that Christians have filled "the very camp", and Eusebius begins his account of the Great Persecution with a purge of Christians from the army.

So the sources record the argument of one side rather than the practice of the whole church. How widely the refusal was held, and whether it was chiefly about killing or about the oath and the idolatry around it, is argued from a thin and one-sided record.

The uncomfortable reading is that a persecuted minority found non-violence easier to hold than an established church responsible for a frontier, and that the theology followed the position.

The reply is that the earlier writers were also objecting to an army whose service meant an oath to the emperor and duties at the temples of the gods, and that removing those removes much of their stated objection, though not Origen’s, which is about blood. Both of those are real arguments and the evidence does not close the gap between them.

Nobody counted. The people who left writing were the ones with a position to defend, and a soldier in Britain or Syria who quietly kept his job left no letter about it.

Most of the record of this question is a record of what a few educated men thought it should be.

The Catholic Church and the Russian Orthodox Church allow that Christians may take part in war, the second while calling war evil. So do three confessions of the sixteenth and seventeenth centuries, in churches that still hold them: the Augsburg Confession in the Lutheran Church–Missouri Synod, the Anglican Articles in the Church of England, and the Westminster Confession in the Orthodox Presbyterian Church. Where criteria are given they descend in part from Augustine, and they are stated as conditions rather than as an endorsement. The Catholic catechism calls them strict: the damage must be lasting, grave and certain, every other means must have been shown ineffective, there must be serious prospects of success, and the arms must not produce evils graver than the evil they answer. Pope Francis wrote in 2020 that it is now "very difficult" to invoke them.

Some refuse war altogether. The Mennonite confession puts it flatly: its members do not prepare for war, or participate in war or military service.

Each side can find its ancestors in the first three hundred years, one in what Tertullian and Origen wrote and the other in the Christians who served anyway. Only one of them has had to govern.