Jeremy Myers has some words to say about Gregory Boyd’s and Walter Wink’s view that political power necessarily corrupts, even demonizes, the Church:
Is There Such A Thing As A Just War?
The “Just War” theory was originally developed by Augustine to defend the Empire’s actions of arresting and killing the Donatists, with whom Augustine was having a theological disagreement. He argued that in certain situations, a war is not wrong if it furthers the cause of Christ and advances the Kingdom of God on earth.
He taught that inflicting temporal pain on someone to help them avoid eternal pain was justified. Also, Augustine believed that since God sometimes uses terror for the good of humans (a questionable premise), the church may also use terror for the sake of the gospel (The Myth of a Christian Nation: How the Quest for Political Power Is Destroying the Church p. 78).
Thanks to Augustine, Christians have been endorsing wars against “Christian enemies” ever since.
But does not the life of Jesus and the truth of the Gospel cry out against this? “Declaring a war just is simply a ruse to rid ourselves of guilt” (Engaging the Powers, p. 225). Such attempts to absolve ourselves from guilt in the murder of others have been around since the very beginning.
The killing of others began in the very first family, when Cain killed Abel.
Why did Cain commit the first murder?
The Bible is rather vague about Cain’s motives, but the root causes appear to be a mixture of jealousy, anger, and the desire for self-advancement. We rightfully condemn Cain for his actions, but when we look at the situation from Cain’s perspective, his murder of Abel was the very first “Just War” in history. Miroslav Volf points out that Cain’s murder of Abel was governed by faultless logic:
Premise 1: “If Abel is who God declared him to be, then I am not who I understand myself to be.” Premise 2: “I am who I understand myself to be.” Premise 3: “I cannot change God’s declaration about Abel.” Conclusion: “Therefore, Abel cannot continue to be” (Miroslav Volf, Exclusion & Embrace, p. 95).
From Cain’s perspective, he had the duty and obligation to protect himself by murdering Abel. If he had admitted that God’s preference for Abel’s sacrifice was correct, then Cain would have had to face his own faults. This he could not do, and so, in self-defense against the moral challenge from his brother, Cain engaged in “Just War” against Abel, and murdered him.
It has been argued that nearly all “Just Wars” in history are of this type. We engage others in a righteous battle, defending our freedoms and liberties, not because the others are necessarily evil and wrong (thought we paint them in this light), but because the only alternative to “Just War” is to admit our own wrongdoing and faults.
And since this is what we will not do, the others must die.
So ultimately, Just War theory is about one thing:
It is either us or them.
There has never been a war in history in which the warriors from both sides did not think their cause was just. In every battle, both sides cry out to their god for victory.
Can we really believe as Christians that since we serve the one true God, our cause is more just than the causes of those we are trying to kill?
Does it not rather seem that if we truly serve the one true God as revealed in Jesus Christ that there would be no cause whatsoever for killing?
When we seek the blood of our enemies, are we not abandoning and forsaking the truth of the shed blood of Jesus, who died for His enemies?
This question boils down to identifying the Biblical definition of justice, and understanding the difference between the God-given domains of Church and State.
The Church advises the state, as Nathan “advised” David. Joseph advised Pharaoh. Daniel advised King Nebuchadnezzar and Mordecai, after repenting, eventually advised Ahasuerus. Justice is a two-edged sword. It involves both vengeance and redemption. To separate one from the other leads to tyranny or anarchy, martial law or lawlessness. The sword of the prophets was the fiery tongue, the God-given Word. The Scriptures make it very clear that the metal swords of these mighty kings were also God-given. 
This explains the difference between murder and killing. Hatred is a crime committed within the domain of the Church. It is slain, mortified, by the Word of God. It leads out of this domain into the domain of the State—murder is a crime punishable by the State, not the Church.
Israel could take up the sword against Canaan because 1) Israel was a Church State, and 2) the Canaanites had broken the “gospel” proclaimed to them by Abraham. This act wasn’t genocide. It was the exercise of the Covenant sanctions. The vengeance carried out under Joshua was a Church-State vengeance. God Himself exercised these same “Church-State” sanctions against Israel through Assyria and Babylon and Rome.
But after the exile, Israel was no longer an autonomous state, and this was by God’s design. Israel herself became the prophetic advisor. She was to be a nation of Nathans. The Church-State commissioned by God, set up under Daniel and decommissioned in AD70/Revelation was a Jew-Gentile one. The Jews could not execute criminals because they were to be a nation of priests. We see the beginnings of this in Ezra, where, all of a sudden, it is not only the genealogies of the priests that matter. By God’s command, they were to submit to their Gentile emperors, and if they did so, they would be exalted into government.  They founded synagogues right across the empire, and this bore fruit, as we see in Acts. But again, they desired a king before God’s time and ended up with a new Saul, the Herods. It took Herod and Pilate, Jew and Gentile, to execute Christ. It took Judah and Rome, Land Beast and Sea Beast, to execute the Firstfruits Church (Rev. 14).
The two-edged sword that the Christian Church wields is the gospel, a Good News which includes bad news, excommunication (which, biblically, is simply preaching of the gospel once again to apostates). This became distorted when the distinct roles of Church and State were conflated. The exaltation of the Church under Constantine was an exaltation by God for her faithfulness unto death.  However, heresy is never to be considered a crime against the State. The inquisitions were the result of a Church overstepping her prophetic demarcation.
So, it is not ungodly for a Christian nation to take up the sword against Muslim invaders, for instance. The question is whether that cause is just. I’m very thankful for the Crusades, and for WWII. And for the Cold War. Perhaps the wars since are more questionable because the West has systematically and institutionally “excommunicated” Christ, as the Herods did, and as the Roman Church did before the Reformation. The problem is not whether “Christian nations” can “Biblically” exist. The problem is Christian nations excluding Christ, forcing Him to knock on the door via His prophets and apostles to serve Covenant papers like a Nathan. 
When Christian Churches, and indeed Christian nations, apostatize, Jesus brings the hordes against them. Most Christians are totally ignorant of the fact that Jesus’ and the apostles’ warnings concerned the end of the Old Covenant in AD70. We can certainly apply these warnings today, but the bloodshed during the siege and destruction in Jerusalem, and indeed right across the entire empire, get overlooked as the actual interpretation. Jesus came again for His own, and poured out the curses of the Mosaic Law for the last time. Jesus and the apostles are portrayed as riding on white horses, with sword-mouths from heaven. That’s the Church power. Unbelieving Judah was being excommunicated from the people of God. And the nations are portrayed with actual swords. That’s State power.  Revelation dealt not only with the hateful hearts of the Jews, but with their “State-sponsored” murders of Christians. As in Joshua, Jeshua circumcised the Church, and the “swarms” marched around and circumcised the City-State of Herodian worship.  That’s what the Revelation is about—the cutting off of The Circumcision.
As in Canaan, the same sanctions executed upon the pagans-under-Covenant can be executed upon apostate Christians. Only, the Covenant territory is now longer limited to Canaan. Jesus rules the world.
The Gospel is the sword of the Church within its God-given domain, and if the Church is doing its job faithfully, it will be exalted as a prophetic advisor to the State, which will result in the State wielding a just sword within its God-given domain. The Gospel will always have State consequences, and to refuse to wield either sword justly is to hand the culture over to Satan.
The Church doesn’t war against flesh and blood. That is the job of the State. But Word inevitably becomes flesh. We must remember that fathers, pastors and soldiers are men who are willing to die for others in their given domains.
Nathan means “gift.” The flaming sword is a gift from God, whether prophetic or kingly. There is no Biblical debate over whether there should be swords, but whether or not those swords are just. The source of this justice is the cross, the bread and the wine, where men and women are slain and resurrected as wise governors in whatever domain God has given them.
The Words of the prophets always precede the swords of the soldiers. If a Christian nation is waging just war, she herself has been “slain.” But if she is waging an unjust war, it is because she is also waging war upon Christ. 
The fact that American troops are forbidden to hand out Bibles in Muslim nations is a dead giveaway. The fact that American troops find themselves hamstrung in conflict by bureaucratic restrictions upon their warfare is also a dead giveaway. A nation that has rejected the Bible understands neither justice nor mercy. When the State ignores the Church, that State is doomed.
 See Church and State.
 See An Excellent Plan and The Restoration Covenant. I highly recommend James Jordan’s commentary on Daniel, available here.
 See A Jew Gets Baptism.
 See The Torah in Revelation.
 See The Fall of Jerusalem [PDF]
 See Circumcision and Apocalypse.
 See The Exorcism of Christ.