Just War Theory of St. Augustine of Hippo

Thinkers in the Western world have examined the ethical questions that are naturally raised by warfare since a very early period in Western history. Arguably, the greatest classical formulation of a theory of just war, including just causes for war and just conduct within war, is found in the work of Cicero, a Roman author of the first century BCE. As the Roman Empire gradually became both officially and majority Christian in Late Antiquity, Christian thinkers began to take up the same questions. While earlier generations of Christians had largely, but not unanimously, been pacifist in orientation, Christian thinkers of the fourth and fifth century, the first to live within the context of a Roman Empire in which the emperors and other government administrators as well as a majority of the population were Christians, found it necessary to reexamine the Christian stance on warfare in the light of the place of Christians in government and the need to defend the interests of the Empire from hostile forces. At the vanguard of this new generation of thinkers was St. Augustine of Hippo, a prominent bishop and a major figure in the history of Latin Christianity. The Just War Theory of Augustine is in many ways a Christian update to the earlier Roman ideas concerning just war, such as those found in the writings of Cicero, but also one that has added important new dynamics to the question of just war, including especially an emphasis on the protection of the weaker members of the societies in conflict, and stands as a landmark and a major influence in the subsequent development of Western approaches to and understandings of warfare.

Early reflections by Greek writers on warfare more often demonstrate, and sometimes applaud, the brutality of war than the possibility of just conduct within it. Homer’s Iliad, composed probably in the eighth century BCE, for example, contains almost no discussion of whether the war about which it was written, the Trojan War, was justified or of whether the participants in the war were just in their conduct. Instead, the author seems to assume warfare as the natural prerogative of upper-class Greek men and that warfare will be governed by very few rules but a great deal of brutality. In Book VI, for instance, the author records the slaying of Adrestus by Menelaus, even after the former had “caught him by his knees” and began “begging for his life.”1 Menelaus hesitated for a moment, considering the possibility of taking Adrestus prisoner in order to exchange him for a ransom later. Agamemnon, Menelaus’s brother, however, persuades him to kill Adrestus, exhorting him not to “spare a single one of them – not even the child unborn and in its mother’s womb; let not a man of them be left alive, but let all in Ilius perish, unheeded and forgotten.”2 There is no mention of any ethical concern in the slaying of Adrestus.

Even those passages of the Iliad which record a resort to mercy and justice within war focus on a sense of personal obligation from one upper-class Greek male to another rather than laws governing one’s conduct within warfare or any overarching ethical concerns. In Book XXIV, for instance, Achilles does not return the body of Hector, the son of Priam, the king of Troy, to his father because such is the ethical course, but because of his respect for the king himself, whom he praises for his “iron courage.”3 Even so, the seeds of the later ideas of Greco-Roman writers are evident. Achilles, for instance, weeps when Priam embraces him because the old man makes him think of his own father and, only a few verses later, he expresses a concern that the gods will punish him if he does not treat Priam well and hand over the body of his son.

These expressions of empathy and the belief that the gods will punish unjust behavior later became the foundation for theories of just war in Roman thought. Later Greek thought, however, did little to develop these concepts. The surviving fragments of the writings of the Presocratic Greek philosophers contain many moral aphorisms and bits of practical wisdom, but no reflection on warfare in relation to their ethical maxims, aside, perhaps, from a few scattered references, such as the saying of Democritus (460-370 BCE), recorded by Plutarch, that men “ought to be instructed in the art of war … which is a source of great and glorious things for men.”4 Other Greek literature, such as plays and histories, similarly contain little development of the idea of justice in relation to war. They do, however, often exhibit the same basic ideas exhibited by Homer and sometimes develop them further. In his play Lysistrata, for instance, Aristophanes tells a story in which the women of Greece decide to withhold sex from their husbands if their husbands do not put an end to war.5

The first relatively full reflection in Greek thought on what makes a war just or unjust is in the writings of Aristotle. In his Politics, Aristotle declares that “the art of war is a natural art of acquisition, an art which we ought to practise … against men who, though they be intended by nature to be governed, will not submit; for war of such a kind is naturally just.”6 This statement, however consonant it may be with the rest of Aristotle’s philosophy as well as with ancient Greek thought in general, does little to provide a practical basis for action or for judging the actions of others. Aristotle’s idea seems to amount to little more than saying that the conqueror was just because he was the stronger and the conquered was unjust because he was the weaker.

It was not until the first century BCE, with the Roman orator Cicero, that Greco-Roman thought had its first advocate of a fully developed theory of just war. His De Officiis contains a lengthy discussion of what constitutes a just reason for war as well as just conduct within war. Although Cicero’s reasoning and examples derive entirely from Roman history, the passage bears a striking resemblance to the fullest biblical explication of just war, the 20th chapter of Deuteronomy. The two passages present an important comparison, both in their similarities and their differences. Perhaps the most outstanding difference is the difference in date of composition. While Cicero, writing in the first century BCE, reflects a long line of development of thinking on war in the Greek and Roman worlds, the Book of Deuteronomy was, according to most historians, written in about the seventh century BCE, only a century after The Iliad and approximately six centuries before Cicero’s life. It is remarkable that the Jews developed a very full theory of just war so much earlier than their Greek and Roman counterparts; this large gap in time may be traceable to the emphasis on ethical conduct from a very early point in biblical thought.7

In spite of the wide differences in time and culture, the two passages are remarkably similar in message. According to Cicero, “we must resort to force only in case we may not avail ourselves of discussion.”8 Similarly, the passage in Deuteronomy orders that “when you approach a city to fight against it, you shall offer it terms of peace,” and only “if it does not make peace with you, but makes war against you, then you shall besiege it.”9 Cicero also advises that “we should spare those who have not been blood-thirsty and barbarous in their warfare.”10 He then gives examples of past Roman conquests and shows that certain cities, because of their rebellious nature, were entirely destroyed while others were spared and sometimes their inhabitants were even made Roman citizens. Deuteronomy, similarly, commands that those who make peace should be spared while among those who fight “you shall strike all the men in it with the edge of the sword” while sparing “the women and the children and the animals and all that is in the city,” taking them as one’s own.11 It is only in those cities from whom the Hebrews fear some particular insidious influence because of “all their detestable things which they have done for their gods” that the Hebrews are told to practice the kind of total war reflected in The Iliad.12 Even in those cases, however, they are warned against scorched earth tactics and destruction of the local environment; the passage rhetorically asks, “is the tree of the field a man, that it should be besieged by you?”13 Cicero offers similar warnings. Both Cicero and the author of Deuteronomy also place an emphasis on ensuring that a war has the support of the religious authorities and is consonant with religious laws, in order to avoid incurring the wrath of the divine.

Although Christianity grew out of both the Greco-Roman and the Jewish cultural traditions, early Christian thinkers largely rejected the ideas of both concerning warfare. Instead, early Christian thought exhibits a markedly pacifist orientation. A passage from the writings of Hippolytus of Rome, an early third century bishop, states clearly a line of thought that runs throughout Christian writings of this period; in discussing the occupations of those who wish to become Christians, he says:

A military man in authority must not execute men. If he is ordered, he must not carry it out. Nor must he take military oath. If he refuses, he shall be rejected. If someone is a military governor, or the ruler of a city who wears the purple, he shall cease or he shall be rejected. The catechumen or faithful who wants to become a soldier is to be rejected, for he has despised God.14

Included alongside soldiers on Hippolytus’s list of those who cannot receive baptism unless they leave their former occupations are pimps, prostitutes, and pagan priests. According to Peter J. Leithart, the “most vigorous and extensive arguments” by early Christian authors against participation in the military “concerned idolatry.”15 “Religion was central to the military life” and Roman paganism pervaded nearly every aspect of it.16 Participation in the Roman military, then, constituted participation in a pagan cult, and therefore apostasy from Christianity and its uncompromising monotheistic stance. The second primary reason for opposition to military service by early Christian authors was the belief in the inherent evil of killing another human being, no matter for how ostensibly noble a cause.

In spite of such strong words by early Christian leaders, there can be little doubt that there were Christians in the military from the beginning of the Christian movement in the first century CE and that their size continued to increase rapidly, just as did the proportion of Christians in the general Roman population. One tantalizing piece of evidence for a growing Christian presence in the military and government is in the beginning of the final and worst persecution of Christians in the Roman Empire, which began under the Emperor Diocletian in about 300; according to the Christian historian Eusebius of Caesarea and other contemporaries of the events, the persecution began with a purge of Christians from the army.17

With the rise of Constantine the Great as the first Christian Roman emperor in the early fourth century, Christianity, which was also quickly becoming the majority religion of the Empire, assumed a new prominence. By the end of the fourth century, under the Emperor Theodosius, Christianity was declared the official religion of the Roman Empire. These drastically changed circumstances brought about a reevaluation of much earlier Christian thought, including thought on warfare.

The Roman Empire was increasingly a Christian empire, and every empire and nation has a need to defend itself. The question Christian thinkers of the fourth century and later had to confront was how this need for defense against invasion by foreign powers and internal insurrection could be reconciled with the ethical demands of the Christian faith. The central reason for opposition to military service by Christians, the avoidance of participation in pagan religion, was removed as an obstacle as paganism was increasingly abandoned or suppressed throughout Roman life, including in the military. The second major reason, the belief that killing another person was inherently immoral no matter the circumstances, remained an obstacle to full participation by Christians in the military, however.

This recognition of a the need for a military and even of the honorableness of military service alongside concerns about taking the lives of other people created a point of tension in Christian thought. This tension is demonstrated in the writings of St. Basil the Great, an influential fourth century Christian bishop from Asia Minor. Basil, in a letter written to a soldier, tells the soldier that “even in a soldier’s life it is possible to preserve the perfection of love to God” and urges him to “play the man” and “be strong.”18 Basil also advised, however, in a different writing, that soldiers who have killed others while at war do not receive the Eucharist for a period of three years “since their hands are not clean.”19

Out of this tension and search for answers in Christian thought, emerged the Just War Theory of St. Augustine of Hippo. The ideas of Augustine, a late fourth/early fifth century Christian bishop in North Africa, have, arguably, had a greater impact on subsequent Christian thought than nearly any other Christian thinker in all of history, aside, perhaps, from the apostle Paul. This is undoubtedly true in regards to his ideas concerning warfare. Augustine drew together the biblical, Greco-Roman, and early Christian strains of thought into a cohesive whole that allowed Christians to define a context for ethical entrance into as well as just conduct within warfare.

Augustine continued in the Christian tradition of believing all war to be intrinsically evil. He offered unequivocal condemnations of those who desired, sought, or enjoyed war, and made it clear that to engage in war justly is to engage in war by force of necessity. In Book 4, chapter 14 of his magnum opus, The City of God, he says “to carry on war and extend a kingdom over wholly subdued nations seems to bad men to be felicity, to good men necessity.”20 Later, in Book 9, chapter 7 of the same work, he states the same even more clearly:

But, say they, the wise man will wage just wars. As if he would not all the rather lament the necessity of just wars, if he remembers that he is a man; for if they were not just he would not wage them, and would therefore be delivered from all wars. For it is the wrongdoing of the opposing party which compels the wise man to wage just wars.21

In all of this, Augustine is not far from and is, in fact, probably drawing upon the ideas of Cicero and the author of Deuteronomy. He goes further than either of them, however, in his condemnation of war itself and in his refusal to allow that the aggressor may be just. For Augustine, war is never a good but only a lesser of evils, and the one who causes the war is always unjust.

Augustine also exceeds both of these earlier ideas of just war in his concern for justice within war. He spends the first seven chapters of Book 1 of The City of God, for instance, maligning the earlier commonly accepted practices of destroying and looting conquered cities, killing, robbing, kidnapping, and raping the inhabitants.22 While, as he admits, this had previously been considered the norm and the prerogative of the victor, he condemns the practice and contrasts it with the mercy and temperance exhibited by Christians in war. In this, Augustine both builds upon and significantly departs from his predecessors in both the Greco-Roman and biblical traditions, both of which allowed for circumstances, however limited, in which it was considered appropriate for the victor to destroy the conquered people entirely. Augustine, in line with earlier Christian tradition, is not willing to make this compromise.

In this blending of the Greco-Roman with the biblical through the lens of the Christian worldview, Augustine forged a new understanding of warfare and of how it can be conducted with justice and especially with an emphasis on mercy. Augustine’s views, influential in this as in all else, came to dominate the Christian understandings of and approaches to warfare. Charlemagne, for instance, the eighth century founder of the Carolingian Empire and one of the most important rulers in European history, “took great pleasure in the books of Saint Augustine and especially in those which are called The City of God,” according to his biographer Einhard.23 In the 13th century, Augustine’s Just War Theory was taken up by the Scholastic philosopher Thomas Aquinas and further elucidated upon by him. Through the work of Aquinas, Just War Theory became part of the official doctrine of the largest Christian organization in the world, the Roman Catholic Church. Augustine’s views were also a major influence on the ideas of the 17th century Dutch Protestant writer Hugo Grotius, whose writings on just war and international relations have influenced nearly every subsequent thinker on the subject and have contributed substantially to the development of modern international law. The modern laws of war, including, for example, the Geneva Conventions, are largely the end-product of the work of Augustine. Through his ability to effectively weave together the various contributing strands of Western Civilization and argue convincingly for his position, the work of St. Augustine of Hippo stands as a monumental achievement and defining moment in understanding war and its relation to ethics. Through his Just War Theory, Augustine’s impact on subsequent thought and conduct in international relations has been tremendous.


1 Homer, The Iliad, tr. Samuel Butler (Chicago: William Benton, 1952), 40.

2 Ibid.

3 Ibid., 176.

4 Plutarch, Against Colotes, 1126A, in Jonathan Barnes, Early Greek Philosophy (New York: Penguin Books, 2001), 229.

5 Aristophanes, The Lysistrata, tr. Benjamin Bickley Rogers, in Robert Maynard Hutchins, ed., Aeschylus, Sophocles, Euripides, Aristophanes (Chicago: William Benton, 1952), 583-99.

6 Aristotle, Politics, Book I, Chapter 8, tr. Benjamin Jowett, in Robert Maynard Hutchins, ed., The Works of Aristotle, Volume II (Chicago: William Benton, 1952), 450.

7 Huston Smith, The World’s Religions: Our Great Wisdom Traditions (New York: HarperCollins, 1991), 275.

8 Cicero, De Officiis, Book 1, XI, tr. Walter Miller (New York: G.P. Putnam’s Sons, 1928), 37.

9 Deuteronomy 20:10, 12 (New American Standard Bible).

10 Cicero, De Officiis, Book 1, XI.

11 Deut. 20:14 (NASB).

12 Deut. 20:18 (NASB).

13 Deut. 20:19 (NASB).

14 Hippolytus of Rome, “The Apostolic Tradition,” 16:9-11, tr. Kevin P. Edgecomb, accessed 24 October 2012, http://www.bombaxo.com/hippolytus.html.

15 Peter J. Leithart, Defending Constantine: The Twilight of an Empire and the Dawn of Christendom (Downers Grove: InterVarsity Press: 2010), 269.

16 Ibid.

l7 Eusebius, The Church History, Book VIII, Chapter IV, 2-3, tr. Philip Schaff, Nicene and Post-Nicene Fathers, Second Serious: Eusebius: Church History, Life of Constantine the Great, Oration in Praise of Constantine, (Peabody: Hendrickson Publishers, Inc., 1994), 326.

18 Basil the Great, in Alexander F.C. Webster and Darrell Cole, The Virtue of War: Reclaiming the Classic Christian Traditions East and West (Salisbury: Regina Orthodox Press, 2004), 70.

19 Ibid., 76.

20 St. Augustine, The City of God, Book 4, Chapter 14, tr. Marcus Dods, in Robert Maynard Hutchins, Augustine (Chicago: William Benton, 1952), 196.

21 Ibid., Book 9, Chapter 7, 515.

22 Ibid., Book 1, Chapters 1-7, 129-133.

23 Einhard, “The Life of Charlemagne,” Book III, tr. Lewis Thorpe, Two Lives of Charlemagne (New York: Penugin Books, 1988), 78

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