I recently finished a paper on the teaching of the early church fathers regarding military service. This list used to be one of the more popular on a previous iteration of my site, so I’m posting it (updated/cited) again. My paper focused exclusively on the pre-Constantinian apostolic fathers and apologists, since a significant ideological shift occurs once the church becomes state-sanctioned. For nearly 3 centuries of Christian history, it was unanimously considered inappropriate for a Christian to serve in the military. It wasn’t even argued about.
There are two basic modes of argumentation. The first (e.g. Tertullian) argues military service splits loyalty between God and the state. The second (e.g. Origen) argues military service is simply inherently wrong because it is violent. Most of the early writers oscillate somewhere in between. (Contra the normal refrain, I couldn’t find an argument that it is wrong due to possibly persecuting fellow Christians, but maybe a minority report exists).
I don’t think it is prudent to build ethics solely on the archaic opinions of our forbearers, but it is interesting to see the difference with the position you get from religious leaders (especially, American) today.
Here they are:
(discussing prostitutes, idol-sculptors, gladiators, astrologers, soldiers, and other professions prohibited to Christians…)
“A soldier of the civil authority must be taught not to kill men and to refuse to do so if he is commanded, and to refuse to take an oath; if he is unwilling to comply, he must be rejected… If a catechumen or a believer seeks to become a soldier, they must be rejected, for they have despised God.”
“And to those who inquire of us whence we come, or who is our founder, we reply that we are come, agreeably to the counsels of Jesus, to ‘cut down our hostile and insolent “wordy” swords into ploughshares, and to convert into pruning-hooks the spears formerly employed in war.’ For we no longer take up ‘sword against nation,’ nor do we ‘learn war anymore,’ having become children of peace, for the sake of Jesus, who is our leader, instead of those whom our fathers followed.”
“…for neither Celsus nor they who think with him are able to point out any act on the part of Christians which savours of rebellion. And yet, if a revolt had led to the formation of the Christian commonwealth, so that it derived its existence in this way from that of the Jews, who were permitted to take up arms in defense of the members of their families, and to slay their enemies, the Christian Lawgiver would not have altogether forbidden the putting of men to death; and yet He nowhere teaches that it is right for His own disciples to offer violence to any one, however wicked.”
Justin Martyr (100-165)
“We who formerly used to murder one another do not only now refrain from making war upon our enemies, but also, that we may not lie nor deceive our examiners, willingly die confessing Christ.”
“We who were filled with war, and mutual slaughter, and every wickedness, have each through the whole earth changed our warlike weapons,— our swords into ploughshares, and our spears into implements of tillage, —and we cultivate piety, righteousness, philanthropy, faith, and hope, which we have from the Father Himself through Him who was crucified.”
“we do not wage war against our enemies,”
“But now inquiry is made about this point, whether a believer may turn himself unto military service, and whether the military may be admitted unto the faith, even the rank and file, or each inferior grade, to whom there is no necessity for taking part in sacrifices or capital punishments. There is no agreement between the divine and the human sacrament, the standard of Christ and the standard of the devil, the camp of light and the camp of darkness. One soul cannot be due to two masters—God and Caesar.”
“To begin with the real ground of the military crown, I think we must first inquire whether warfare is proper at all for Christians. What sense is there in discussing the merely accidental, when that on which it rests is to be condemned? Do we believe it lawful for a human oathto be superadded to one divine, for a man to come under promise to another master after Christ?... Shall it be held lawful to make an occupation of the sword, when the Lord proclaims that he who uses the sword shall perish by the sword? And shall the son of peace take part in the battle when it does not become him even to sue at law?... Indeed, if, putting my strength to the question, I banish from us the military life…”
“What man of sound mind, therefore, will affirm, while such is our character, that we are murderers? For we cannot eat human flesh till we have killed some one… How, then, when we do not even look on, lest we should contract guilt and pollution, can we put people to death?”
Arnobius (d. 330)
“We, a numerous band of men as we are, have learned from His teaching and His laws that evil ought not to be requited with evil, that it is better to suffer wrong than to inflict it, that we should rather shed our own blood than stain our hands and our conscience with that of another.”
“I do not wish to be a king; I am not anxious to be rich; I decline military command… Die to the world, repudiating the madness that is in it.”
“But if the law of liberty, that is, the word of God, preached by the apostles (who went forth from Jerusalem) throughout all the earth, caused such a change in the state of things, that these [nations] did form the swords and war-lances into ploughshares, and changed them into pruning-hooks for reaping the corn, [that is], into instruments used for peaceful purposes, and that they are now unaccustomed to fighting, but when smitten, offer also the other cheek, then the prophets have not spoken these things of any other person, but of Him who effected them.”
Clement of Alexandria (150-215)
“Let the Athenian, then follow the laws of Solon, the Argive those of Phoroneus, and the Spartan those of Lycurgus. But if you record yourself among God’s people, then heaven is your fatherland and God your lawgiver.”
“For we are not to delineate the faces of idols, we who are prohibited to cleave to them; nor a sword, nor a bow, following as we do, peace.”
Martin of Tours (316-397)
“Hitherto I have served you as a soldier; allow me now to become a soldier to God. Let the man who is to serve you receive your donatives. I am the soldier of Christ; it is not lawful for me to fight.”
A few more that I did not have space for in my paper:
Clement of Alexandria
“Above all, Christians are not allowed to correct with violence.”
“Whatever Christians would not wish others to do to them, they do not to others. And they comfort their oppressors and make them their friends; they do good to their enemies…. Through love towards their oppressors, they persuade them to become Christians.”
Ignatius of Antioch
“There is nothing better than peace, in which all warfare of things in heaven and things on earth is abolished.”
“We would rather shed our own blood than stain our hands and our conscience with that of another. As a result, an ungrateful world is now enjoying–and for a long period has enjoyed–a benefit from Christ. For by his means, the rage of savage ferocity has been softened and has begun to withhold hostile hands from the blood of a fellow creature. In fact, if all men without exception…would lend an ear for a while to his salutary and peaceful rules,…the whole world would be living in the most peaceful tranquility. The world would have turned the use of steel into more peaceful uses and would unite together in blessed harmony.”
Cyprian of Carthage
“Wars are scattered all over the earth with the bloody horror of camps. The whole world is wet with mutual blood. And murder–which is admitted to be a crime in the case of an individual–is called a virtue when it is committed wholesale. Impunity is claimed for the wicked deeds, not because they are guiltless, but because the cruelty is perpetrated on a grand scale!”
Archelaus, "Disputation of Archelaus and Manes"
“Those soldiers were filled with wonder and admiration at the grandeur of the man’s piety and generosity and were struck with amazement. They felt the force of this example of pity. As a result, many of them were added to the faith of our Lord Jesus Christ and threw off the belt of military service.”
Athenagoras of Athens, "A Plea for the Christians"
“We have rejected such spectacles as the Coliseum. How then, when we do not even look on killing lest we should contract guilt and pollution, can we put people to death?”
 Origen. “Against Celsus,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 4 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf04.html (accessed May 16, 2012), 1291.
 Ibid., 1051.
 Justin Martyr. “The First Apology,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 1 (Grand Rapids: Christian Ethereal Library, 1885) http://www.ccel.org/ccel/schaff/anf01.html (accessed May 16, 2012), 465.
 Justin Martyr. “Dialogue With Trypho,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 1 (Grand Rapids: Christian Ethereal Library, 1885) http://www.ccel.org/ccel/schaff/anf01.html (accessed May 16, 2012), 678.
 Tertullian. “Treatise on Idolatry,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 3 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf03.html (accessed May 16, 2012), 148.
 Tertullian. “Treatise on the Crown,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 3 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf03.html (accessed May 16, 2012), 206-7.
 Athenagoras. “A Plea for the Chrisitans,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 2 (Grand Rapids: Christian Ethereal Library, 1885) http://www.ccel.org/ccel/schaff/anf02.html (accessed May 16, 2012), 331.
 Arnobius. “Against the Heathen,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 6 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf06.html (accessed May 16, 2012), 934.
 Tatian. “Address to the Greeks.” In Ante-Nicene Fathers, ed. Philip Schaff. Vol. 2 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf02.html (accessed May 16, 2012), 133.
 Irenaeus. “Against Heresies,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 1 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf01.html (accessed May 16, 2012), 1271.
 Jean-Michel Hornus, It Is Not Lawful for Me to Fight: early Christian Attitudes Toward War, Violence, and the State (Scottdale: Herald Press, 1980), 102.
 Clement. “The Instructor,” in Ante-Nicene Fathers, ed. Philip Schaff. Vol. 2 (Grand Rapids: Christian Ethereal Library, 1885), http://www.ccel.org/ccel/schaff/anf02.html (accessed May 16, 2012), 611.
 Ibid., 94.