I have been working something over for a while regarding Christians and the sword. As kind of an intro, see the below article from the Schleitheim Confessions, the 1527 doctrinal statement of Swiss Anabaptists led by Michael Sattler:
VI. We are agreed as follows concerning the sword: The sword is ordained of God outside the perfection of Christ. It punishes and puts to death the wicked, and guards and protects the good. In the Law the sword was ordained for the punishment of the wicked and for their death, and the same (sword) is (now) ordained to be used by the worldly magistrates.
In the perfection of Christ, however, only the ban is used for a warning and for the excommunication of the one who has sinned, without putting the flesh to death - simply the warning and the command to sin no more.
Now it will be asked by many who do not recognize (this as) the will of Christ for us, whether a Christian may or should employ the sword against the wicked for the defense and protection of the good, or for the sake of love.
Our reply is unanimously as follows: Christ teaches and commands us to learn of Him, for He is meek and lowly in heart and so shall we find rest to our souls. Also Christ says to the heathenish woman who was taken in adultery, not that one should stone her according to the Law of His Father (and yet He says, As the Father has commanded me, thus I do), but in mercy and forgiveness and warning, to sin no more. Such (an attitude) we also ought to take completely according to the rule of the ban.