This question has caused a lot of division in the body of Christ. Should a Christian go to war where he might kill other people when the Bible says to "turn the other cheek" (Luke 6:29)? Is it right to do war against others or does the Bible forbid it?
War is a state of declared, open, and armed conflict between two or more nations. It is sometimes undertaken in self-defense such as when the U.S. entered WWII as a result of Japan attacking Pearl Harbor. Other times, however, nations unjustly go to war to take spoils from other countries. Murder, on the other hand, is an unlawful taking of life and is always wrong. When nations go to war, it is declared lawful by the countries going to war -- sometimes for moral reasons and other times for immoral reasons. Therefore, and immoral war could be considered a form of murder where a moral war could be in self defense. But not all war is wrong.
It is difficult to determine when war would be a righteous endeavor given that leaders of nations are not Christian and could easily have ungodly reasons for going to war. Nevertheless, war is an unfortunate reality in this world and it causes great destruction, misery, and loss of life. It should be avoided if possible and undertaken only as a last resort.
The Bible teaches that we have the right to self defense, Exodus 22:2: "If the thief is caught while breaking in, and is struck so that he dies, there will be no blood guiltiness on his account." The Bible also tells us to protect the innocent, Deut. 19:10, "So innocent blood will not be shed in the midst of your land which the Lord your God gives you as an inheritance, and blood guiltiness be on you." Also, see "Fathers shall not be put to death for their sons, nor shall sons be put to death for their fathers; everyone shall be put to death for his own sin," (Deut. 24:16). If we were to apply these principles to war, I would conclude that war is justifiable when it is in self defense and/or when it is to protect the innocent. Therefore, a Christian could rightfully engage in war given those conditions.
More on war
We can see that war is not a sin in itself since in the Old Testament God sends people into war:
- "Then the Lord spoke to Moses in the plains of Moab by the Jordan opposite Jericho, saying, 51 "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. 4"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. 2 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; 4 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, 14 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.