Theology is developed out of real-world experiences in response to real-world challenges. Christian attitudes toward war and military service provide an excellent case study – before St. Augustine first developed the idea of a Just War, early Christian attitudes toward war evolved significantly during the first centuries after Jesus, and arguably, the most significant factor was Christianity’s changing relationship with Empire.
First of all, early Christians lived in two worlds. First, their “Jewish” world, especially from the Hasmonean period onward, provided plenty of examples of armed rebellion, revolt, and all-out war. In many of the extant sources from this context, violent rebellion was viewed positively, often as a sign of faithful obedience to the Law, or as an instrument to mete out God’s justice by punishing the unrighteous. 1 Maccabees provides plenty of great examples, for instance 3:3-8 praises a Hasmonean patriarch for attacking the Seleucids:
[Judas Maccabeus] brought greater glory to his people. In his armor, he was like a giant. He took up his weapons and went to war; with his own sword he defended his camp. He was like a ferocious lion roaring as it attacks. Judas hunted down those who broke the Law and set fire to all who oppressed his people… We will praise him forever for what he did. He went through the towns of Judea and destroyed all the godless men. He relieved Israel of its terrible suffering.
But early Christians also lived in the rapidly-Romanizing Hellenistic East, where war was often seen as a tool for preservation of peace and justice. In fact, precursors for Just War Theory can be traced through Plato, Aristotle, Thucydides, and other Greek writers, as well as Roman writers like Cicero, especially his De officiis. Moreover, military service was an opportunity to augment and exhibit one’s status. Kings often gifted veterans with tracts of land following successful military campaigns, while Book 40 of Cassius Dio’s Roman History catalogs other forms of honor that could be bestowed on soldiers:
they adopted a middle course, and by praising some of them and not others, by allowing some to wear garlands of olive at the festivals and others not, and, furthermore, by voting to some of them ten thousand sesterces and to others not a copper….
Against this background, it is important to note that there was no official “Christian” stance on war. Instead, there were many competing conceptions of morality, relation to the State, and comfort level with assimilating to the surrounding culture. Literature surviving from the 1st and 2nd centuries offers varying opinions – some glorifies martyrdom (and by extension, passive resistance) as the supreme act of faithfulness to God. Famously, the Martyrdom of Polycarp (c 150) and the Letter of Ignatius to the Romans (c 110) show this clearly, while the latter text depicts soldiers as unnecessarily cruel beasts. Other texts highlight the uncompromising rejection of imperial authority. In The Acts of the Scillitan Martyrs (c 180), a disciple named Speratus announces, “I do not recognize the empire of this world. Rather I serve the God whom no one has seen…”
Likely these latter texts come from settings where Christians were suffering from some form of persecution. Contrary to the romanticized belief that Rome uniformly saw Christians as dangerous enemies of the State, persecution was unevenly seen across the empire, and it seems one of the most common causes of this was that Christians were withdrawn and nonparticipants in larger society: they “assemble in stealth” and “refrain from honest pleasures”;
they “do not go to our shows [and] take no part in our processions, [they] are not present at our public banquets, [they] shrink in horror from our sacred games… [they] do not bind [their] heads with flowers [or] honor your body with perfumes” (Octavius of Minucius Felix, c 200?).
Ostensibly this suggests that Christians abstained from military service as well.
Later texts, however, go out of their way to show that Christians were beneficial, integrated participants in broader society. Justin Martyr says in his First Apology that Christians are “helpers and allies in promoting peace”, and Tertullian even writes in his Apologeticus 42 (c 200) that Christians “sail with you and serve in the army and we till the ground and engage in trade as you do” (the first clear extant textual evidence of Christians in the military). Tertullian’s later opinions, however, are mixed – De Corona 11 seems to be primarily concerned about the “lawlessness” and dubious lifestyles associated with soldiers, while Idololatria 19 sounds like Tertullian is categorically denouncing all military service: “No dress is lawful among us, if assigned to any unlawful action.” In any case, there surely were Christians serving in the military by this point, and Tertullian’s hostility towards that fact suggests that his feelings were not universally shared among all Christians.
In another well-known passage from about the same period, Hippolytus’ Apostolic Traditions (c 215) provide guidelines about who should be accepted to the catechumenate:
A military man in authority must not execute men. If he is ordered, he must not carry it out. Nor must he take military oath. If he refuses, he shall be rejected. If someone is a military governor, or the ruler of a city who wears the purple, he shall cease or he shall be rejected. The catechumen or faithful who wants to become a soldier is to be rejected, for he has despised God.
This passage also mentions sculptors, charioteers, gladiators, and prostitutes, and the overriding concern seems to be ensuring Christian conduct is seen as undeniably moral and upright. But the document is also peculiar in that the actual proscription against soldiers actually seems to be about murder, not military service itself – though the distinction may be difficult to maintain in practice.
Christianity became more “compatible” with war in 312 when emperor Constantine saw a heavenly vision on the battlefield and commanded his soldiers to add Christian symbols to their shields. This, according to Eusebius of Caesarea, was the beginning of Constantine’s conversion to Christianity – after he defeated (and decapitated) his rival Maxentius, Constantine ended his patronage of the traditional Roman religions and slowly shifted his support to Christianity.
By 380, the Edit of Thessalonica required all Roman citizens to profess faith in Christianity. But after Rome was attacked in 410, Augustine’s City of God, relieved the theological tension between Christian pacifism and military service by providing the rationalization of a Just War. He argued for a fundamental spiritual/secular split to reality – we live in the City of Man that is beset by violence and injustice, but Christians also live in the hidden, spiritual City of God. Though our citizenship is secure in the latter, sometimes we “gotta do what we gotta do” to get by in the former: “War is justified only by the injustice of an aggressor; and that injustice ought to be a source of grief to any good man, because it is human injustice,” as Augustine writes in Part 5, Book XIX.
It was a clever theological move that helped Christians adapt to the new world they found themselves in, and it has held sway with Christians ever since.