In AD 218, early Church Father, Hippolytus said this about those being converted from the broader Roman world to the new community of Christianity:
"The professions and trades of those who are going to be accepted into the community must be examined. The nature and type of each must be established... brothel, sculptors of idols, charioteer, athlete, gladiator... give it up or be rejected. A military constable must be forbidden to kill, neither may he swear; if he is not willing to follow these instructions, he must be rejected. A proconsul or magistrate who wears the purple and governs by the sword shall give it up or be rejected. Anyone taking or already baptized who wants to become a soldier shall be sent away, for he has despised God."
Not too long after this was written, Christians decided to rethink their commitment to the cross. Constantine and his minister of proganda, Augustine reworked parts of Christian doctrine and practice and reversed the status of Christianity, from oppressed to oppressor.
If you think about it, it's quite ironic that Constantine saw an image of the cross before the battle of the Milvian Bridge. The cross of Jesus is an act of laying down one's life to save the lives of your enemies while war is the act of killing your enemies to save your own life or the lives of those close to you.
Other than small Jesus-movements here and there, like the Mennonites or groups like Simple Way or Christian Peacemaking Teams, Christianity has never really recovered from Constantine removing the cross and replacing it with the sword. Although, I believe there is a change happening. I believe a lot of people are being freed from their cultural constructs and re-discovering the teachings of Jesus. As Shane Claiborne wrote, "we can admire and worship Jesus without doing what he did. We can applaud what he preached and stood for without caring about the same things. We can adore his cross without taking up ours."
And to quote Soren Kierkegaard,
"The matter is quite simple. The Bible is very easy to understand. But we Christians are a bunch of scheming swindlers. We pretend to be unable to understand it because we know very well that the minute we understand, we are obliged to act accordingly. Take any words in the New Testament and forget everything except pledging yourself to act accordings. My God, you will say, if I do that my whole life will be ruined. How would I ever get on in the world? Herein lies the real place of Christian scholarship. Christian scholarship is the Church's prodigious invention to defend itself against the Bible, to ensure that we can continue to be good Chrisitians without the Bible coming too close. Oh, priceless scholarship, what would we do without you? Dreadful it is to fall into the hands of the living God. Yes, it is even dreadful to be alone with the New Testament."
And to quote Claiborne one more time, "When it comes to the world's logic of redemptive violence, Christians have a major stumbling block on their hands - namely, the cross.
There comes a point where we recognize we're trying to serve two masters, and we have to choose which one we will serve. Our arms are just not big enough to carry both the cross and the sword.
We can learn from the bloody pages of history. The more vigorously we try to root out evil by force, the more evil will escalate. For every Muslim extremist killed, another is created. Likewise, the more passionately we love our enemies, the more evil will diminish. This is also the story of the martyrs - for every Chrsitian killed at the hands of evil, another would rise up, converted by their faithful self-sacrificial love. And historically, Christianity spreads most rapidly when we are killed at the hands of evildoers without retaliating. It's the story of the growth of the church during the great persecutions. They wrote that for every one of them who was killed, there were ten converts. As the saying goes, 'In the blood of the martyrs is the seed of the saints.' The paradox is that the church is healthiest during eras of persecution, and it gets sick during periods of comfort and ease and power."