From the article, What Did Jesus Have to Do with Violence? By Mark Durie

Although the Old Testament does condone the use of force to purge a land of violence and injustice, the Bible’s attitude to such violence is not that it is sacred or holy.  On the contrary, King David, who fought many wars with God’s active support and guidance, was not allowed to be the one to build god’s temple in Jerusalem, because there was so much blood on his hands.

Violence is regarded by the Bible as an inherently evil symptom of the corruption of the whole earth after the fall: “the earth was filled with violence” (Gn 6:11).  In contrast, the prophet Isaiah looked forward to the day when the days of violence would be no more. Isaiah describes the Lord’s anointed as unacquainted with violence: “They made His grave with the wicked, and with a rich man at His death, although He had done no violence and had not spoken deceitfully” (Is 53:9).

In this way the Old Testament sets the scene for the revelation of Jesus Christ.  The key question for Christians is “What did Jesus have to do with violence?”  When we turn to consider Jesus and His followers, we find a systematic rejection of religious violence. Jesus’ message was that His kingdom would be spiritual and not political.  Jesus explicitly and repeatedly condemns the use of force to achieve His goals: “Put your sword back in place because all who take up a sword will perish by a sword” (Mt 26:52)…..

As Jesus went to the cross, He renounced force, even at the cost of His own life: “My kingdom is not of this world…If My kingdom were of this world, My servants would fight, so that I wouldn’t be handed over to the Jews.  As it is, My kingdom does not have its origin here” (Jn 18:36)…..

At one point Christ said, “Don’t assume that I came to bring peace on the earth.  I did not come to bring peace, but a sword.” (Mt 10:34)  This is sometimes cited by anti-Christian apologists as evidence for Jesus’ militancy, but the statement occurs in an extended passage where Jesus is advising His disciples on the inevitability of persecution.  The sword He refers to is the one which will be raised against them.  ….

Jesus’ take on violence was reinforced by the apostles Paul and Peter, who urged Christians to show consideration to their enemies, renounce retaliation, live peaceably, return cursing with blessing, and show humility to others (Rm 12:14-21; Ti 3:1-2; 1 Pt 2:20-24).  They also allowed that the (most likely pagan) civil authorities would need to use force to keep the peace and this role should be respected (Rm 13:1-7; 1 Pt 2:13-17).  This was an extension of the earlier Jewish position that Jews should submit to the rule of law in whichever country they find themselves, even if the king was a pagan (Jr 29:4-7).

The New Testament supports the just use of force as a proper function of the state, whatever its religious identity.  Thus it is not a specifically religious or sacred act to go to war or to use force to implement justice.  It is just a matter of public duty, one aspect of the ordering of society which God has established for the common good.  Fighting may be considered just, not because it is advancing any one faith over another, but because it is warranted and conducted according to principles of justice applicable to all people.

If only Christians had maintained this New Testament position down the centuries, the world would have been a better place. The invention of “Christendom” in the fourth Christian century, and the later influence of a centuries-long struggle against the Islamic jihad, ultimately led Christians to develop aberrant theologies that regarded warfare against non-Christians as “holy,” and soldiers who died fighting in such wars were regarded as “martyrs.” Thankfully, this view of warfare has been universally denounced in the modern era as incompatible with the gospel of Christ.