Yes many groups of Christians become pacifists in theory and some actually in practice like the Quakers. Christians however as a group never were completely non-violent. Jesus didn't teach solders to quit their job just not to extort yet he very clearly didn't preach harming others in revenge. The church at Jerusalem began with the death penalty. A few years later in the Pauline epistles acts of the government were ordained as well. The Old Testament of course is filled with by God's permission. In summary some believers may be pacifists but God, Jesus and the Holy Spirit surely are not though they very rarely enact such severe punishment.
Mat 5:38 Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth:
Mat 5:39 But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also.
Act 5:5 And Ananias hearing these words fell down, and gave up the ghost: and great fear came on all them that heard these things.
Rom 13:4 For he is the minister of God to thee for good. But if thou do that which is evil, be afraid; for he beareth not the sword in vain: for he is the minister of God, a revenger to execute wrath upon him that doeth evil.
ESV Luk 3:14 Soldiers also asked him, “And we, what shall we do?” And he said to them, “Do not extort money from anyone by threats or by false accusation, and be content with your wages.”
Rev 19:15 And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.