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Just War Theory

War is on the minds of all Americans today. Like it or not, we are at war with Islamist terrorists in Afghanistan and Iraq.

  • Kenneth L. Gentry, Jr., Th.D.,
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War is on the minds of all Americans today. Like it or not, we are at war with Islamist terrorists in Afghanistan and Iraq. Questions regarding these conflicts encourage us to look deeper into the foundational questions about the legitimacy of war.

The Prince of Peace

Christians serve the One prophesied to come as the “Prince of Peace” (Is. 9:6) who was to effect peace (Is. 2:4). His birth was announced by angels as seeking to establish peace: “Glory to God in the highest, and on earth peace among men with whom He is pleased” (Lk. 2:14).

In keeping with prophetic pronouncement and angelic declaration, Christ’s teaching confirms His peaceable intent. We serve a Savior who teaches us “all things whatsoever ye would that men should do to you, do ye even so to them” (Mt. 7:12).1 He commands in Matthew 5:44: “Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you.” He was so insistent upon this that He taught us: “whoever slaps you on your right cheek, turn to Him the other also” (Mt. 5:39).

Some Christians take the Lord’s peaceable teachings to entail pacifist obligations. They believe that faithful Christians never support war in any context. They often cite Christ’s “turn the other cheek” as “obvious” evidence for this. They do not realize that He actually said: “whoever slaps you on your right cheek, turn to Him the other also.” For someone to “slap” you on the right cheek would mean that he was giving you a backhanded slap (in that most people are right handed and would slap with the right hand). Christ is speaking of a personal confrontation seeking to settle differences with a fight. This personal directive does not speak to conflicts on the national level involving security concerns.

Despite widespread and simplistic opinion, Christ’s teaching is much broader than “turn the other cheek.” It is all-encompassing, providing direction for all areas of life: spiritual and physical, personal and social, economic and educational — and yes, even political and judicial.

Jesus’ first recorded public discourse opened with a confirmation of the entire Old Testament revelation, including the Mosaic Law (His primary focus): “Do not think that I came to abolish the Law or the Prophets; I did not come to abolish, but to fulfill. For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass away from the Law, until all is accomplished. Whoever then annuls one of the least of these commandments, and so teaches others, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven” (Mt. 5:17-19). Elsewhere He rebukes those who do “not know the Scriptures” and He affirms the Old Testament by other means (Mt. 22:29; cp. Mt. 4:4, 7, 10; Jn. 3:10; 10:35). So what does the Old Testament teach us about war?

The Old Testament and War

The Old Testament endorsed at least certain forms of war. Abram is commended for his war against the evil kings: “Blessed be Abram of God Most High, possessor of heaven and earth; and blessed be God Most High, who has delivered your enemies into your hand” (Gen. 14:20). Of Moses we read: “Moses built an altar, and named it The Lord is My Banner; and he said, ‘The Lord has sworn; the Lord will have war against Amalek from generation to generation’” (Ex. 17:15-16). Even the Psalmist David writes in a worship song: “Blessed be the Lord, my rock, who trains my hands for war, and my fingers for battle” (Ps. 144:1; cp. 2 Sam. 22:35; Ps. 18:34).2

But God’s law does not endorse all war. The Scriptures teach principled war, laying down rules for establishing a just war (jus ad bellum). The Christian view was well stated by the great scholar Augustine in keeping with the overarching peaceable intentions of Christ: “War is waged in order to attain peace.” Because of the sinfulness of man, sometimes war is the way to peace.

In a time when our country is at war, we need to reflect upon the principles of just war that have long been a part of the Christian worldview. The average Christian has only a general, foggy notion of the principles of Just War Theory — if any notion at all.

Just War Theory Summarized

In keeping with the peaceable intentions of the Christian faith, Just War Theory posits the following principles:

(1) The Principle of Just Cause. A just war can only be fought to right a grievous wrong and must be engaged with a view to redressing that injury. The right to personal self-defense is always just. We see this legally stated on the personal level in God’s law: “If the thief is caught while breaking in, and is struck so that he dies, there will be no blood guiltiness on his account” (Ex. 22:2). We see it on the social level in granting the magistrate the right to capital punishment for prescribed crimes: “He who strikes a man so that he dies shall surely be put to death” (Ex. 21:12).

God condemns “princes [who] are like wolves tearing the prey, by shedding blood and destroying lives in order to get dishonest gain” (Eze. 22:27). The encoding of legislation in the law regarding national armies takes the personal and local right to self-defense to the national level: “Then Amalek came and fought against Israel at Rephidim. So Moses said to Joshua, ‘Choose men for us, and go out, fight against Amalek’” (Ex. 17:8-9; cp. 1 Sam. 30:3, 18-19). The blessings of God include victory against the enemy who assails: “The Lord will cause your enemies who rise up against you to be defeated before you; they shall come out against you one way and shall flee before you seven ways” (Dt. 28:7). Even the New Testament commends just war by placing in the “Hall of Faith” those who “became mighty in war, put foreign armies to flight” (Heb. 11:34).

(2) The Principle of Last Resort. In international relations when tensions are raised, Just War Theory seeks to insure peace and safety. Just war can only be waged as a last resort, requiring that all reasonable non-violent options must be exhausted before the use of force can be justified. Even about cities that threatened Israel we read: “When thou comest nigh unto a city to fight against it, then proclaim peace unto it. And it shall be, if it make thee answer of peace, and opens unto thee, then it shall be, that all the people that is found therein shall be tributaries unto thee, and they shall serve thee. And if it will make no peace with thee, but will make war against thee, then thou shalt besiege it” (Dt. 20:10-12).3

(3) The Principle of Legitimate Authority. A war is just only if it is waged by a legitimate authority. Vigilante justice and gang warfare are not God-ordained means of social conduct. They are debilitating features of social chaos evidencing the breakdown of moral order.

Even just causes require just means of resolution. To plan war is to plan death, which requires duly sanctioned moral authority. This is held only by the civil magistrate, who is ordained to wield the sword in defense of its citizenry.

According to Romans 12:19, vengeance belongs to God who will repay the evildoer. Just three verses later Paul says that God has given the right to avenge wrongdoing to the civil magistrate who is the “minister of God” in this respect ( Rom. 13:1-4). “Governors [are] sent by him for the punishment of evildoers and the praise of those who do right” (1 Pet. 2:14), which includes punishment of whole nations that threaten evil against another nation.

(4) The Principle of Successful Prospect. A war can only be just if it is fought with a reasonable chance of success. Human life is precious, in that man is created in the image of God (Gen. 1:26-27). God has a special concern for man, His highest creature: “What is man, that Thou dost take thought of him? And the son of man, that Thou dost care for him?” (Ps. 8:4). God ordains the protection of human life: “Whoever sheds man’s blood by man his blood shall be shed, for in the image of God He made man” (Gen. 9:6). This, of course, prohibits suicide, even at the national level.

In a parable, Jesus touches on this principle of war: “Or what king, when he sets out to meet another king in battle, will not first sit down and take counsel whether he is strong enough with ten thousand men to encounter the one coming against him with twenty thousand?” (Lk. 14:31). David expresses a concern for the prospect of utter defeat: “David inquired of the Lord, saying, ‘Shall I pursue this band? Shall I overtake them?’ And He said to him, ‘Pursue, for you shall surely overtake them, and you shall surely rescue all’” (1 Sam. 30:8).

The righteous seek safety, not destruction: “My God, my rock, in whom I take refuge; my shield and the horn of my salvation, my stronghold and my refuge; my savior, thou dost save me from violence. I am saved from my enemies” (2 Sam. 22:3-4). Consequently, wide-scale deaths and injury incurred in a hopeless cause are not morally justifiable, being a form of national suicide.

(5) The Principle of Peaceful Objectives. The ultimate goal of a just war is to re-establish peace and safety. The historical goal of the Kingdom of God clearly teaches this primary historical objective: “He will judge between the nations and will render decisions for many peoples; and they will hammer their swords into plowshares, and their spears into pruning hooks. Nation will not lift up sword against nation, and never again will they learn war” (Is. 2:4). As a counter-example, Islam as a religion and culture has from its founding in Muhammad until the present been in a constant state of war with other cultures.4

The just war goal of securing peace embodies the Biblical principle that we should “not be overcome by evil, but overcome evil with good” (Rom. 12:21). David, though a “man of war” (1 Chr. 28:3), exhibits his righteous desire for peace: “Too long has my soul had its dwelling with those who hate peace. I am for peace, but when I speak, they are for war” (Ps. 120:6-7). Rushdoony observes: “Even in wartime, God’s purpose, the furthering of life for the purposes of godly dominion, must be obeyed.”5

(6) The Principle of Proportionate Means. Just war is God-sanctioned violence. But the violence meted out in war must be proportional to the injury suffered. For instance, the laws governing capital punishment constrain the state by not allowing the magistrate to capitally punish a thief (Ex. 22:7) or to put to death the murderer’s family: “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” (Dt. 24:16).6 Likewise, the aim of war must be constrained by principles of proportionality, according to the lex talionis principle of “an eye for an eye” (Ex. 21:24; Lev. 24:20f).

Rushdoony observed, “[T]otal war is prohibited, either against man or against his land.”7 Napoleon’s utter humiliation of his enemies led to the Prussian military instructor, Karl von Clausewitz, developing the concept of “total war.” But God’s law forbids total war: “When you besiege a city a long time, to make war against it in order to capture it, you shall not destroy its trees by swinging an axe against them; for you may eat from them, and you shall not cut them down. For is the tree of the field a man, that it should be besieged by you? Only the trees which you know are not fruit trees you shall destroy and cut down, that you may construct siegeworks against the city that is making war with you until it falls” (Dt. 20:19-20).

(7) The Principle of Civilian Immunity. When just war is waged, military plans and actions must discriminate between combatants and non-combatants. Unarmed civilians are never legitimate targets of war, and every reasonable effort must be taken to avoid killing them. Civilian deaths are tolerable only as accidental, unavoidable collateral damage resulting from an attack on a legitimate military target.

The Scriptures reflect this principle in various places. Armed combatants are the target of just war: “Let not him who bends his bow bend it, nor let him rise up in his scale- armor; so do not spare her young men; devote all her army to destruction” (Jer. 51:3). “When the Lord your God gives it into your hand, you shall strike all the men in it with the edge of the sword. Only the women and the children and the animals and all that is in the city, all its spoil, you shall take as booty for yourself; and you shall use the spoil of your enemies which the Lord your God has given you” (Dt. 20:13-14). Again, this embodies the principle of man being the image of God and under His protection.


These principles, long maintained in Christian culture and established in Biblical law, must guide us in one of the most fearsome powers of government: the right to wage war. God’s Word directs us in all of life, and is especially important in governing that which can end life and culture.


1. We must be careful to interpret Jesus’ teaching from within His God-based worldview. For instance, this directive is not to be used with rapists, sodomites, and sado-masochists.

2. This psalm was left out of Roman Catholic peace activist Father Daniel Berrigan’s commentary on the Psalms.

3. Israel had God-defined borders (Gen. 15:18; Ex. 23:31; etc.) and could never legitimately possess imperialistic pretensions. This passage is not dealing with the special, limited Holy War which secured the Promised Land: “Thus you shall do to all the cities that are very far from you, which are not of the cities of these nations nearby” (Dt. 20:15).

4. See my article on the Chalcedon website which shows the inherently destructive character of Islam: “Christ, Muhammad, and the Culture of Beheading.”

5. Rousas John Rushdoony, Institutes of Biblical Law (Vallecito, CA: Ross House Books, 1973), 355.

6. Those who claim court-ordered capital punishment is merely revenge encoded in law must recognize severe limits on the offended: they cannot punish the criminal immediately (without trial), torture him, punish his family, or do anything beyond the limits of the law. Capital punishment actually curtails personal revenge.

7. Rousas J. Rushdoony, The Institutes of Biblical Law (Vallecito, CA.: Ross House Books, 1973), 355.


  • Kenneth L. Gentry, Jr., Th.D.

Kenneth L. Gentry, Jr., holds degrees from Tennessee Temple University (B.A.), Reformed Theological Seminary (M. Div.), and Whitefield Theological Seminary (Th. M.; Th. D).  He also attended Grace Theological Seminary for two years.  He is Research Professor in New Testament (Whitefield Theological Seminary), a theological writer, and conference speaker. He has written numerous books and articles on issues such as theology, ecclesiology, eschatology, theonomy, six-day creation, presuppositionalism, worldview, Christian education, and more.  He also offers a Christian writing correspondence course.  He is the Director of GoodBirth Ministries, a non-profit religious educational ministry committed to sponsoring, subsidizing, and advancing serious Christian scholarship and education.  He is a retired Presbyterian minister holding his ordination vows in the Reformed Presbyterian Church, General Assembly.

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