"for the battle is not yours, but God's."2 Chronicles 20:15..".."For the LORD your God is he that goeth with you, to fight for you against your enemies, to save you.(Deut.20:4)
In the Old Testament God sends HIS people into war:
"Then the Lord spoke to Moses in the plains of Moab by the Jordan opposite Jericho, saying, "Speak to the sons of Israel and say to them, "When you cross over the Jordan into the land of Canaan, 52 then you shall drive out all the inhabitants of the land from before you, and destroy all their figured stones, and destroy all their molten images and demolish all their high places; 53 and you shall take possession of the land and live in it, for I have given the land to you to possess it." (Num. 33:50-53).
In fact, God uses war as a means of disciplining nations.
"I sent a plague among you after the manner of Egypt; I slew your young men by the sword along with your captured horses, And I made the stench of your camp rise up in your nostrils; Yet you have not returned to Me, declares the Lord." (Amos 4:10).
Also, the Lord is called a warrior.
"The Lord is a warrior; The Lord is His name. "Pharaoh's chariots and his army He has cast into the sea; And the choicest of his officers are drowned in the Red Sea." (Exodus 15:3-4).
From this we can easily conclude that going to war is not a sin, that is, if it complies with the biblical instructions of self-defense and protection of the innocent.
Furthermore, Christians are instructed to be in subjection to the governing authorities whose establishment is from God. This establishment has the right to declare war and to punish its citizenry--even by capital punishment.
"Let every person be in subjection to the governing authorities. For there is no authority except from God, and those which exist are established by God. Therefore he who resists authority has opposed the ordinance of God; and they who have opposed will receive condemnation upon themselves. 3 For rulers are not a cause of fear for good behavior, but for evil. Do you want to have no fear of authority? Do what is good, and you will have praise from the same; for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath upon the one who practices evil." (Rom. 13:1-4).
"Submit yourselves for the Lord's sake to every human institution, whether to a king as the one in authority, or to governors as sent by him for the punishment of evildoers and the praise of those who do right." (1 Peter 2:13-14).
Finally, notice that some soldiers approached John the Baptist and inquired about repentance. John did not tell them to stop being soldiers but to do their jobs properly--honestly.
"And some soldiers were questioning him, saying, "And what about us, what shall we do?" And he said to them, "Do not take money from anyone by force, or accuse anyone falsely, and be content with your wages." (Luke 3:14).
From all of this, we can see that going to war is not wrong it itself and that a Christian can go to war under the right circumstances.
We are to preserve life, this is a principle carried over from the Old Testament. The use of physical force to protect or defend another is not an alternative but a command.
We protect our children from drug dealers and pedophiles and all other sort of lowlifes. We lock our doors of our homes. We are to be vigilant against evil and take precautions to prevent it. We will keep our car keys on our person, we do not leave them in the ignition switch saying I have trust. We do what we can so we do not become sick. We do preventative measures for our safety.
If we watch someone steal something and do not speak up or we know of a crime we could prevent, we are complicit to the crime. To watch an act of cruelty to children without trying to intervene is morally inexcusable. To permit a murder to take place when we could have done something to prevent it is ethically wrong. If we fail to use force to protect another whom is confronted with evil we are in fact failing to show love toward them. It would instead be sin to sit by idly and watch another harm physical harm perpetrated on them when it can be avoided or prevented by force. Not resisting evil is a sin of omission, and a sin of omission can bring the same result as one committing evil. Any man who refuses to protect his wife and children against a violent intruder fails in his moral obligation.
Is violence never a justified act? What of self-defense? Do we stand by and watch someone being abused or physically threatened with harm?
We are to pursue peace, but tolerance, finding compromise condoning criminal activity or withholding punishment does not lead to peace. It is the greatest act of love to sacrifice your life to protect the innocent, to defend their freedom against oppressors when they can’t. Self-sacrifice is part of the definition of agape? But what about sacrificing one self for the enemy? This is what Jesus did. We were all enemies before we became friends.
If one believes killing is one and the same as murder, then no one would be allowed to us deadly force, even in defense to save lives. The Bible prohibits murder, but not in using killing against a hostile enemy; neither is the ownership and use of weapons are not prohibited. There were times when it became necessary for Israel to fight or go into captivity. The other exception is when God decided to punish Israel for their disobedience and told them to go into captivity so they would live.
In Gen.14 Abraham rescued lot by a battle when he was forcefully taken. Israel battled against her enemies in Deut.20:1, 29:7, Joshua 11:15 the battle of Jericho,vs.20, Joshua 12. In Numbers 35:17 it explains by having the intention to kill, murderers were to be put to death. In Deut. 16:18-19 they were commanded to cast out all their enemies. Killing is different than murder. Murder is senseless and for selfish reasons, while killing is to protect and preserve life.
The Israelites had to take possession of the Promised Land by conquest. They engaged themselves in continued bloody wars with the Canaanite tribes. Except in the case of Jericho and Ai, the war did not become aggressive until after the death of Joshua. Up until then the attack was always first made by the Canaanites. Israel was employed by God to sweep them away off the face of the earth. They were relentless enemies. Israel always had a regimented army, they had Compulsory service in1 Samuel 14:52, there were Captains of fifties 2 Kings 1:9; Isaiah 3:3, Captains of hundreds Numbers 31:14,48; 2 Kings 11:15; 1 Chronicles 28:1; 2 Chronicles 25:5, Commander-in-chief 1 Samuel 14:50; 2 Samuel 2:8; 8:16; 17:25; 19:13; 20:23. Generals of corps and divisions Numbers 2:3,31; 1 Chronicles 27:1-22; 2 Chronicles 17:12-19 Captains of thousands Numbers 31:14,48; 1 Samuel 17:18; 1 Chronicles 28:1; 2 Chronicles 25:5. It is for this reason they have survived as a people even to today.
"How could God be called 'good' if He forbade His people to protect their wives from ravishment and strangulation by drunken marauders, or to resist invaders who have come to pick up their children and dash out their brains against the wall? No policy would give freer rein to wickedness and crime than a complete surrender of the right of self-defense on the part of the law-abiding members of society. No more effective way of promoting the cause of Satan and the powers of hell could be devised than depriving law-abiding citizens of all right of self-defense. It is hard to imagine how any deity could be thought 'good' who would ordain such a policy of supine surrender to evil as that advocated by pacifism. All possibility of an ordered society would be removed on the abolition of any sort of police force. No nation could retain its liberty or preserve the lives of its citizens if it were prevented from maintaining any sort of army for its defense. It is therefore incumbent on a 'good God' to include the right of self-defense as the prerogative of His people. He would not be good at all if He were to turn the world over to the horrors of unbridled cruelty perpetrated by violent and bloody criminals or the unchecked aggression of invading armies.
Not only is a proper and responsible policy of self-defense taught by Scripture from Genesis to Revelation, but there were occasions when God even commissioned His people to carry out judgment on corrupt and degenerate heathen nations and the complete extermination of cities like Jericho (cf. the article on "Was Joshua justified in exterminating the population of Jericho?" in connection with Joshua 6:21). The rules of war laid down in Deuteronomy 20 represented a control of justice, fairness, and kindness in the use of the sword, and, as such, they truly did reflect the goodness of God.
Special hardship conditions were defined as a ground for excusing individual soldiers from military duty until those conditions were cleared up (Deuteronomy 20:5-7). Even those who had no such excuse but were simply afraid and reluctant to fight were likewise allowed to go home (Deuteronomy 20:8). Unlike the heathen armies, who might attack a city without giving it an opportunity to surrender on terms (cf. 1 Samuel 11:2-3, 30:1-2), the armies of Israel were required to grant a city an opportunity to surrender without bloodshed and enter into vassalage to the Hebrews before proceeding to a full-scale siege and destruction. Even then, the women and children were to be spared from death and were to be cared for by their captors (Deuteronomy 20:14). Only in the case of the degenerate and depraved inhabitants of the Promised Land of Canaan itself was there to be total destruction; a failure to carry this out would certainly result in the undermining of the moral and spiritual standards of Israelite society, according to Deuteronomy 20:16-18. (This corrupting influence was later apparent in the period of the judges (Judges 2:2-3, 11-15)"
I think Archer makes some very good points. When we look at war in the Bible, such as the verses in Deuteronomy, they are actually defensive in nature and not offensive. These areas of the Hittites, Amorites, Canaanites, Perizzites, Hivites and Jebusites were morally corrupt and would have destroyed the Israelis, if left alive. God did not set the Israelis to conquer other nations this way. If you will notice, He didn't say now after that go into Asia, Europe, and Africa and take those ones out too. There has always been a buffer zone around the country of Israel because this land was promised to them by God. In order to keep the borders clean from attack and moral corruption they had to defend themselves. Hence, the creation of a buffer zone. It should be noted that the Israelis were to make peace before they went into battle, as well (Deuteronomy 20:10).
God allowed his people's to form a Army to protect his people and go to battle.(Num.1:1-34,Num.31:1-54,Deut.20:1-20)