What is the genealogy of the just war tradition? If we trace its roots, will we find them planted in religious or secular soil? The answer is “both.” The just war tradition emerges primarily from two streams of thought: the ancient Graeco-Roman world and the biblical writers of the Old and New Testaments. This is not to say that elements of just war thought are not found in other cultures or traditions. In fact, one can discern just war thinking at work in Eastern philosophers such as Lao Tzu, Sun Tzu, and the Hindu Book of Manu. Yet, the tradition is firmly rooted in the Graeco-Roman tradition and the Bible.

Just War in the Graeco-Roman Tradition

The Greek roots of the just war tradition can be excavated by traveling back to 413 BC, when we find a Greek leader, Nikolaos, addressing the Sicilian assembly after vanquishing the Athenians, in the Second Battle of Syracuse, during the Peloponnesian war. Nikolaos argued that “common usage of the Greeks forbids the slaughter of the vanquished,” and thus that “magnanimity will be the best way to establish peace and make the Athenians ashamed of their unjust war.”

Similarly, we find Greece’s greatest philosopher, Plato, outlining criteria for justice in warfare. In the concluding dialogue of Republic, he implies that it is an unjust cause for a nation to wage war primarily to enrich itself. He also implies that the only legitimate authorities are the persons who are wisest and most able to make such a decision. Additionally, he argued that military victors must not enslave or slaughter those who they conquer, given that such actions would make it difficult to achieve an enduring peace after the war. Finally, he argued that warfighters must discriminate between the “guilty” and the “innocent,” refusing to kill the latter.

When we turn to Rome, the roots of the just war tradition are best revealed in the emergence of a first-rate political leader, Marcus Tullius Cicero, who was also a first-rate philosopher of just war. In On Duties, he articulates principles that remain part of the just war tradition today: he argues that war should be waged with the aim of peace, it must be a last resort, it must be preceded by a formal declaration of war, and that armies must treat prisoners of war in a fair and humane manner. Finally, and most significantly, he insisted that the moral and humane treatment of people should not only be applied to the privileged elite, but to all of humanity.

War and Peace in the Old Testament

The just war tradition is rooted not only in the Graeco-Roman tradition but also in the Jewish and Christian Scriptures. God’s revelation to Israel repeatedly addressed the need to act justly in every dimension of national life. The prophet Micah’s charge to Israel is illustrative: “Mankind, [the Lord God] has told each of you what is good and what it is the Lord requires of you: to act justly, to love faithfulness, and to walk humbly with your God.”

The biblical witness is, however complex and multi-faceted. Individual texts about warfare must be placed within their broader biblical and historical context. Especially significant is the fact that, at first blush, some Old Testament passages—such as Moses’ defeat of the Midianites and Joshua’s defeat of Ai—seem to support a crusade ethic for today. However, a close examination of the biblical message reveals that crusade warfare is forbidden in our era. God alone can pronounce instructions for a total war as justified, and he alone can lead such a war. (God’s epistemic vantage point renders his pronouncements justified; he knew with certainty the threat that the Canaanites posed to his people and their mission.) Thus, in an era in which God does not speak directly to political leaders, as he sometimes did to Israel’s leaders, we are forbidden from engaging in total warfare as crusaders hold.

Additionally, when Israel was waging war, God normally called it to adhere to certain rules of engagement. A good summary of some of those rules is found in Amos 1:3-2:3, in which the Lord rebukes the nations for war crimes. He rebukes Damascus for threshing the defeated people of Gilead with iron sledges; Gaza for exiling whole communities in order to sell them; Tyre for breaking treaties; Edom for letting his anger rage unchecked and for attacking “his brother” (i.e. Edom was related to Israel); and the Ammonites “because they ripped open the pregnant women of Gilead in order to enlarge their territory.”

Despite the violence its critics usually point to as evidence of justifying a crusader ethic, the Old Testament regularly laments the tragic necessity of war. The Psalmist laments, “Too long have I lived among those who hate peace. I am for peace; but when I speak, they are for war” (120:6). Yet, it also recognizes that nations sometimes must wage war and that honorable soldiers should be honored for their military service. Shammah is honored for standing his ground in the middle of the battlefield even when many of his fellow soldiers fled, thus incurring the Lord’s blessing for the army of Israel (2 Sm. 23:12). Beniah the son of Jehoiada is also honored among David’s men for killing two of Moab’s special operators (2 Sm. 23:20-23). Other examples abound. The message is clear: honor should be given to soldiers who exhibit courage, persistence, and skill in battle.

War and Peace in the New Testament

Unlike the Old Testament, the New Testament contains no narratives of wars in past history. Yet, it does address warfare from multiple angles. This brief article will select a few of those angles for brief summary: the legitimacy and authority to wage war, the law of love in relation to war, and limitations on the use of the sword.

Various New Testament passages speak to the legitimacy of a just war and the proper authority to wage such a war. The classic passage is Romans 13:1-7, in which the apostle Paul makes clear that governing authorities are “established” by God and that rulers should be a “terror…[to] those who do wrong.” Another passage is Luke 14:31-33, in which Jesus commends a hypothetical king for waging war only when he has determined that success is probable and the projected good achieved would be greater than what it will cost to achieve it.

One of the biblical passages about the law of love is Romans 12:9-13:10 in which Paul encourages Christians to love one another, live in harmony, and refrain from taking revenge. With the same quill, however, Paul declares that God commissions political leaders to wield the sword to protect good persons and punish wrongdoers. The interpersonal law of love, therefore, is not at odds with the political use of the sword.

There are limitations, however, to the use of the sword. The fact that God authorizes government to use the sword does not mean that any or every use of the sword is just. Jesus rebuked Peter for using the sword to expand the church’s mission (Mt 26:47-56). Similarly, Paul forbids the Roman church from rebelling against the government.


The principles for just war have been espoused in many historical and cultural contexts, but most especially in the Graeco-Roman, Jewish, and Christian traditions. These principles can be discerned by all humanity, not merely those who have biblical revelation, and thus are binding on all people. What the biblical narrative makes clear, however, is that war and injustice are the result of human sin, and God has provided civil government as a means of minimizing the effects of such sin through the use of the sword. We love God and our neighbors best when employ force according to his instructions, including when to go to war and how to conduct ourselves in the midst of war.

Other articles in the “Ethics of Warfare” Series:

1. To Fight or Not to Fight? That is the Question.

2. What Kind of Peace Should America Seek in our War-Torn Era?

3. Why I am Peaceful but Not a Pacifist

4. Why I am Not a Jihadi

5. Why I am a Proponent of the Just War Tradition

6. The “Founding Fathers” of the Just War Tradition

7. Seven All-Stars of the Just War Tradition

8. Eight Recent Champions of the Just War Tradition

9. 8 Criteria for Deciding When It’s Right to Go to War

10. 7 Moral Criteria to Guide Commanders during Battle

11. How Do Just War Principles Apply to Terrorism & Asymmetrical Warfare?

12. How Do Just War Principles Apply to Drone Warfare?


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