Many in the early Church were explicitly against war and violence, to a degree that might shock many contemporary Christians. The relationship between our faith and government, violence, war, defense, are all tricky issues. They are issues that I have been wrestling with a great deal lately, and which I have been researching (at least in terms of early Christian views on these issues). Scholars disagree on the nature of this pacifism in the early Church. Some argue that they were more concerned about the idol worship associated with being in the army than a condemnation of violence per se. I am quite convinced by George Kalantzis's (of Wheaton College) new book (Caesar and the Lamb) arguing, to the contrary, that an overwhelming majority (practically unanimous) of the Fathers were solidly against violence itself; they were rather explicit about it.
Regardless, these issues are tricky. It was much easier to be a pacifist when Christianity was a minority religion in a pagan empire. When Christians gained political clout and eventually became the majority, these questions became a lot more complicated. So, like I said, it's tricky.
I don't presume to give an answer, but a few reflections.
Many in the early Church held to a deep sense of hope that I think is sometimes lacking in the Church today. While living in an empire that persecuted them, tortured them, killed them, and that operated on war and power and greed, the early Church had hope because they knew that they were the living body of the resurrected Christ. Christ had died and been raised again. This was a solid fact to stand upon. A solid hope in the midst of all the darkness. A brand new world was breaking forth into the old one, and everything was different now. The power of God had been unleashed on earth and death itself had been turned upside down. Carl F. H. Henry put it well: "The early Christians did not say ‘look what the world is coming to!’ but ‘look what has come into the world!’"
When it came to their views of violence, they were wildly full of hope. Violence and death are not parts of the world God intended; and they had hope that God can and would put all things to right. A hope grounded in the resurrection. Miracles can happen. They have happened. Things can change.
Perhaps we have learned some valuable lessons and gained a wise caution, by having a bit more reserve about how imminent we understand the Kingdom to be, than many early Christians possessed. Seeing the Kingdom as too imminent (or imminent in the wrong ways) has led to some great atrocities. Many of early Christians (up until the 3rd century or so) believed the end was right around the corner. We no longer think this way and often talk about the way things 'must be' until the end comes. There is some wisdom here, but this can often be rather fatalistic in a way that I don't think is Biblically warranted.
There needs to be some balance. But I think we could use a healthy dose of their hope.
We may decide that violence is a necessary evil until the end is actually here. We may not be able to agree with many early Christians' almost entirely unequivocal pacifism. But there is something from them to learn. If we decide to believe that war is a necessary evil, let us never forget that it is still an evil, and that we are given power in Christ to pursue a different way. We must be spokespeople for peace, and for hope.
I will leave you with a paraphrase of the words of Origen (3rd century). Origen had seen a lot of violence. His father was violently persecuted while Origen was but a boy. His spiritual mentor was also killed, along with many others in the city in which Origen was living. Yet, he remained hopeful about a different way to live in the world.
A man by the name of Celsus had written a long treatise condemning Christianity on a variety of levels. We don't have the original document - we only know that Origen responded (extensively) to Celsus several years later, and his response has been preserved. This is my paraphrase of a part of that response:
"Celsus has argued that we are detrimental to the wellbeing of society, because we refuse to fight in the emperor's armies. 'If everyone became Christians,' he argues, 'the empire would collapse because there would be no army.'
Celsus, don't you understand? We are actually the best soldiers the emperor has. We take up arms with something much more powerful than a sword. We wage war with prayer. We do battle against the forces of evil which are the true and ultimate source of violence. We pray for peace. We pray for the advancement of the Gospel of peace to all people. And we live and pray knowing that our God has already won the victory."
He who lives by the sword shall die by the sword. He who dies by the sword shall live, and shall conquer. Indeed 'more than conquerers.'
We live in the hope of the resurrection, the hope that there is a power greater than the sword that will, and can, beat spears into pruning hooks. That is the power of God.