It almost goes without saying that peace is revered in Christianity, and this was the case (as far as can be told) from its earliest movements. Its core scripture is full of teachings that promote peace, condemn violence, and are fully pacifistic in nature. Among them (verse citations in brackets are Old Testament quotations, references or allusions):
[Jesus said,] “Blessed are the peacemakers, for they shall be called sons of God.” (Mt 5:9)
[Jesus said,] “You have heard that it was said, ‘An eye for an eye, and a tooth for a tooth’ [Ex 21:23-25, Lv 24:19-20, Dt 19:21]. But I say to you, do not resist an evil person; but whoever slaps you on your right cheek, turn the other to him also. If anyone wants to sue you and take your shirt, let him have your coat also. Whoever forces you to go one mile, go with him two.” (Mt 5:38-41)
And behold, one of those who were with Jesus reached and drew out his sword, and struck the slave of the high priest and cut off his ear. Then Jesus said to him, “Put your sword back into its place; for all those who take up the sword shall perish by the sword [Gen 9:6]” (Mt 26:51-52)
[Jesus said,] “But I say to you who hear, love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you. Whoever hits you on the cheek, offer him the other also; and whoever takes away your coat, do not withhold your shirt from him either. Give to everyone who asks of you, and whoever takes away what is yours, do not demand it back.” (Lk 6:27-30)
Never pay back evil for evil to anyone. Respect what is right in the sight of all men. If possible, so far as it depends on you, be at peace with all men. Never take your own revenge, beloved, but leave room for the wrath of God, for it is written, “Vengeance is Mine, I will repay,” says the Lord [Dt 32:35]. (Rom 12:17-19)
All of this is fully in line with the Jewish apocalypticism from which most of the early Christian movements emerged. With the Forces of Darkness in charge of the world (according to this school of thought), fighting back against it was useless. Things would be set right when God finally intervened and set things right — and he was going to do it very soon. Anything else was, simply, foolish.
Of course, the world in which Christianity originated changed. And as the Christian movements expanded, they also evolved. The religion’s focus had been on its presumed founder, Jesus of Nazareth in Galilee, who’d been executed by Roman occupiers at the instigation of the Jewish priesthood and authorities.
It was from this perspective, coupled with the apocalyptic philosophy, that pacifism made sense. Rome and its legions controlled the world. They worked hand-in-hand with the Jewish authorities. Why fight them? Any such effort was fruitless, until things were set right again. And things weren’t going to be put right, until God saw fit to put them right. This reasoning was effectively bolstered by the results of the Roman-Jewish war of the 60s CE which ended with the destruction of Jerusalem in 70 CE and the razing of the Jews’ Temple.
While the very first generation of Christians did view the Roman regime as hostile and resented Rome’s occupation, as the religion’s reach extended within the Roman Empire and it seeped into more sectors of Greco-Roman society — both societally and geographically — this perspective made less sense. Romans were converting to the religion in ever-larger numbers. The religion’s attitude toward them evolved, because (literally) it had to.
At the same time, the world itself changed. Rome increasingly looked less and less like the undefeatable power it had been thought of (and had wished the world to see it as). The end of the Pax Romana in the late 2nd century and later the Crisis of the Third Century made clear that Rome was extremely flawed. Civil wars large and small erupted as usurping emperors attempted to seize power. At the same time, external enemies pressed in from the outside, causing no small amount of problems.
While pacifism made sense to people convinced their deity would set the world right (probably in a colossal, even catastrophic way) in short order (as in, within the next few months or at most a couple of years), as the decades and even centuries rolled by without any such thing occurring, this sort of thinking became untenable.
The hope of living in a peaceful world in which violence was merely a bad dream, had long proved an impossibility. Critics of Christianity often derided the faith based on its reverence for pacifism, viewing it as foolish. Over time, some Christians would come to agree with that assessment.
Despite this shift, reverence for peace and peacemakers remained a hallmark of Christianity. Christians continued to honor scripture (such as I quoted above) that focused on it. The problems of their world, as well as of the Roman Empire, weren’t limited to wars (both internal and external). Other problems cropped up; disasters such as plagues, earthquakes, floods, famines, etc.
Life could be harsh in many ways; violence (including warfare) was but one harsh aspect of it they had to pay attention to. Overall, Christianity continued to view wars of any kind as an evil in and of themselves.
Scholars generally attribute Christianity’s change in attitude toward war to St Ambrose of Milan even though he was not the first Christian thinker to address the subject. He was, however, in a position to give voice to some new thinking about war.
He’d been born into a prominent Gallic Roman family (though of Greek descent) that had already been Christian for some time. As a child his family relocated to Rome. In his 30s he became governor of Liguria, of which Milan was its seat.
As a native of Gaul and a Roman official with connections to the Imperial court (Milan had been Rome’s western capital since the time of Diocletian), Ambrose’s perspective on war no doubt differed from that of previous Christian thinkers. His views were not extensively developed, however.
It might best be said of Ambrose’s approach to war, as a Christian, was that it could be a necessary evil. That is, war remained an “evil” to be avoided to whatever extent was possible. But defensive wars were potentially acceptable, so long as they allowed for a just outcome.
He also believed violence could address heresy. However, his record on this matter isn’t entirely clear. For example, he’d opposed the secular trial, and execution, of the heretic Priscillian. But with that said, he certainly did not approve of Priscillian or his movement.
Although Ambrose had given it its first major boost, the “just war” theory gained considerably more traction within Christianity at the hands of his student and protégé St Augustine, about whom I’ve also written. He took Ambrose’s concepts and built upon them, especially in light of the sack of Rome by the Vandals in 410 CE.
This event shattered the Greco-Roman world in many ways, even though the city of Rome itself was no longer a true capital — it had remained, in the view of society, the Empire’s “center” intellectually, socially, and culturally. Rome’s fall inspired Augustine to write De civitate Dei (or The City of God) and it was here that he best outlined his thoughts on the matter.
For him, wars could be “just” only so long as they met certain criteria:
It goes without saying that much of the warfare that had been conducted in Augustine’s time wouldn’t have lived up to all of this. Certainly the imperial contenders who’d fought one another would never have qualified; their wars weren’t waged by legitimate rulers (on at least one side).
On the other hand, efforts to put down those usurpers, as well as the defense of Rome in the face of Vandal invaders, would have met Augustine’s standards as “just wars.”
As the Middle Ages unfolded and rolled on, the “just war” theory remained part of Christianity. It was commented on and refined over time, but always built upon the foundation established by Ambrose and Augustine.
It ended up being included within St Thomas Aquinas’s massive tome Summa Theologica. There, it was set in stone within western Christendom. As such it was based on three primary Augustinian points: “Just wars” had to be waged with virtuous intent and in the name of promoting peace; they had to be ordered by rightful leaders; they had to be carried out in the name of a just cause or to right a wrong.
This remains, more or less, Roman Catholicism’s teaching on the subject, even now in the 21st century.
That’s not to say this was the only form of Christian thinking on the matter. There remained within Christendom a strain of pacifist thinking about war, through the Middle Ages and even into modern times, which rejected the “just war” theory, either partially or in toto. Sects such as the Quakers and Mennonites (for example) were (and are still) notably pacifist.
The Commandment against killing was most often cited as the reason wars should never be waged. Augustine and others who promoted the “just war” concept countered that God’s instruction to kill wasn’t to be taken as strictly or as literally as would first appear.
Even today one sees Christians who respond that the Commandment should better be understood as “thou shalt not murder” rather than “thou shalt not kill.” God had never intended, this reasoning goes, to forbid self-defense. This of course is belied by Jesus’ own reported admonition never to resist evil people and always to “turn the other cheek.”
As a religion, and overall, Christianity is conflicted on the matter of war. Ostensibly it opposes war, but it in most regards — and according to the majority of its sects — it’s viewed as acceptable under certain conditions, very much in the vein of Ambrose and Augustine’s reasoning. Christians can claim to oppose war generally, yet still find ways to justify fighting whenever they need to, in spite of Jesus’ reported teachings in the Sermon on the Mount (and the Sermon on the Plain).
That’s not to say all Christians think this way. As noted, some have rejected war. This has led to some of them being conscientious objectors during military drafts. A noted example was a Seventh-Day Adventist, Desmond Doss, who refused to use or even carry a weapon in World War II but did become a medic and saved many lives. Another was an Austrian Catholic, Franz Jägerstätter, who ultimately was executed by the Third Reich for refusing to fight for the Nazis.
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