In this essay, I will examine two of the predominant Christian thinkers from the early developers of JWT. Three contemporary authors will also be examined as well such as; Jeff McMahan, Michael Walzer, and Michael Farrell. The intent is to discover credible sources and look for logical moral consistency throughout the works of several resources and attempt to contribute further insight. Just War Theory has an esteemed past with early developmental figures such as St. Augustine of Hippo and St. Thomas Aquinas. Naturally, wars have been prominent prior to Augustine and Aquinas; and wars are prominent in our present days such as post 911 wars of Afghanistan and Iraq. The consistency of wars has motivated the novelties of more contemporary authors such as Michael Walzer, Jeff McMahan, and Michael Farrell. There are many more scholars and examiners of JWT who have added their own insights to further develop popular JWT concepts such as Jus ad Bellum and in bello. Jus post-Bello is a modern concept dealing with how to rebuild a nation after destroying it.

Preceding Thinkers

St. Augustine is perhaps not only a significant figure in Christian theology, but some secular philosophers may consider him as one of the most important philosophers of the western philosophical tradition. Augustine’s philosophy is so profound that some may consider St. Augustine as the leader of just war theory development. St. Augustine in his time was keen on understanding the dilemma of a just war, and approaches the topic with the intent of resolving the dilemma with great intellectual ambition.

Perhaps the best place to begin a study of just war theory is with St. Augustine. Director of the Countering Weapons of Mass Destruction Graduate Fellowship Program and Senior Research Fellow at the National Defense University Center for the Study of Weapons of Mass Destruction, Dr. John Mark Mattox, author of, Saint Augustine and the Theory of Just War, Bloomsbury Publishing Plc, 2006. ProQuest Ebook Central examines the writings of Augustine and attempts to systematically reflect the thought of Augustine as it pertains to JWT. According to Mattox, it presented an overwhelming challenge for him as he realized how the complexities of Augustine’s thoughts were interrelated with many of his other doctrines. Although many may relatively enjoy the insight in Dr. Mattox’s account of Augustine’s JWT, Dr. Mattox personally felt he did not meet his personal goal in attempting to capture Augustine’s philosophy completely.

One of the unique contributions of Mattox is that he developed a few tables which compared the different views of Augustine, Ambrose, and Cicero in relation to the JWT principles of jus ad Bellum. Dr. Mattox lists the principles as; just cause, comparative justice, right intention, competent authority, public declaration, and last resort. Augustine, Ambrose, and Cicero had similar reasoning toward the jus ad Bellum principles; nevertheless, it is effortlessly noticeable how the concepts of the three thinkers and especially Augustine influenced modern political doctrine as it is reflected in current political doctrine.

Over 800 years after the death of St. Augustine; Thomas Aquinas arguably follows as one of the next best Catholic theologians and philosophers to contribute to the doctrine of JWT. In one of Aquinas’s voluminous books, The Summa Theologica Article 1. Question 40. Page 3074,  “whether it is always sinful to wage war,” St. Aquinas reveals astounding insight on the topic of war. It is perhaps in the best interest of the reader to primarily focus on article one to gain a strong perspective on Aquinas’s justification for war. In addition to article one, Aquinas writes four articles in total regarding war and its justifications; whether it is lawful for clerics to fight in war, whether it is lawful for belligerents to lay ambushes, and whether it is lawful to fight on holy days.

It is very interesting to consider the format in which Aquinas decided to articulate his thoughts. It may seem safe to infer that Aquinas formulated his articles exemplifying historical religious catechisms. His first question of whether it is always sinful to wage war is in a curious form. Gregory M. Reichberg, Adjunct Professor, the Department of Political Science at the University of Oslo. Head of the Research School on Peace and Conflict; author of Thomas Aquinas Just War and Pacifism. Professor Reichberg in his book argues that Aquinas was making the point that waging war is always sinful; nevertheless, there are occasions when going to war is justified. Furthermore, in his book he builds a case against those who may misinterpret Aquinas’s writings as encouraging pacifism.

Aquinas raises objections to his questions in his articles to communicate his viewpoints.  For a better understanding of Aquinas’s writing, it may help to view his opening question in article one as a proposition instead of a question. For example, instead of “whether it is always sinful to wage war” one may rephrase it too, “it is always sinful to wage war” then followed by objection one and two and etc. The objections are against the proposition that it is “always sinful to wage war;” based on the objections that follow, it is implying that there are justifications for waging war. This rephrasing of the question, I believe may help to dissuade anyone who may believe Aquinas may have been writing from the basis of pacifism.

Make no mistake, Aquinas does entirely build the case that killing and waging war is entirely wrong, yet the justifications for war become evidently clear with great reason. Aquinas in the first four objections references a few passages of scripture, yet the interpretations and reflections he uses to justify warfare may appeal to those who seek a philosophical answer to JWT. As Aquinas continues, he frequently quotes sermons from Augustine to further elaborate justification for waging war and for the justification of Christians involved in Soldiering as careers.

In particular, something not commonly read about is the justification for Soldiers to take part in military actions, especially whether Christians ought to involve themselves in military affairs. Aquinas references one of Augustine’s sermons on the son of the centurion. Aquinas highlighted Augustine’s reference of Christ impressing on Soldiers to restrain from evil against others and be content with their wages. Aquinas uses Augustine’s sermon to propose Christians and all may indeed become Soldiers and be involved in warfare if necessary; otherwise, Christ would have commanded them to forsake their service, instead, He suggested to be content with their wages, implying they may continue to serve in the military; in relation, Dr. John Mattox, Saint Augustine and the Theory of Just War Bloomsbury Publishing, exemplifies a similar example from Augustine. A Soldier by the name of Boniface reveals to Augustine that he wants to leave the military life for a life of religious service. Augustine advises Boniface that although a life of religious service would be greater than a military one, he would be of better service to God if he stayed in the military considering the Vandal invasion.

Contemporary Thinkers

In general, when studying JWT it is noticeable that most researchers agree humans killing humans is one of the most immoral actions displayed by human nature, and objectively wrong. Yet, most JWT researchers have agreed that when involved in a war it becomes morally permissible for humans to kill humans on a large scale. Jeff McMahan is a contemporary philosopher and author who presents a contrasting view of popular JWT beliefs. On the subject of Just War Theory Jeff McMahan authored Killing in War, Oxford University Press USA – OSO, 2009. ProQuest Ebook Central. Jeff McMahan’s intent is to reveal that the conditions of war do not justify the killings involved during wartime. In McMahan’s perspective, the conditions for killing in war are no more permissible than the conditions of humans killing humans in the context of individual murder or self-defense. McMahan believes that merely because some politicians allowed the country to go to war; does not give that country the moral permission to oppress the objective moral rights of people in a different country.

The book is written in only five chapters, yet it is 250 pages because of several subsections in each chapter. The first 37 pages of chapter one revolve around the morality of participating in an unjust war. Examples of being involved in an unjust war include violations of the principles mentioned earlier in the essay. The 66 pages of chapter two pertain to the popular doctrines and arguments for the moral equality of combatants. Chapter three has three subsections that have subsections to the three subsections attributing to a thorough explanation of the popular excuses offered for the unjust combatants. Chapter four is perhaps the most relevant portion of the book. McMahan writes in great detail about the various types of threats and how these stipulations are used to excuse unjust combatants for their actions. McMahan finishes the book with chapter five considering the status of civilians in a state of war. McMahan clarifies issues such as civilian liabilities, immunities, collateral damage, whether or not civilians can be open to military attacks, and furthermore; McMahan also gives attention to the topic of terrorism late in chapter five.

Another contemporary philosopher, professor, and author of over two dozen books; Michael Walzer has written on the subject of JWT in 1977 with a second edition published in 1992; Just and Unjust Wars : a Moral Argument with Historical Illustrations. 2nd ed. New York: Basic Books, 1992. Print, and a fifth edition published in 2015. The first publication published in 1977 was based on Walzer’s reflections from the Vietnam War. The book may be considered as one of the standards pieces of literature written on the topic of JWT.

About almost 100 pages more than Jeff McMahan’s Killing in War, Michael Walzer gives greater detail in the philosophy of JWT from a political activist perspective with references to historical authors of JWT. References of other examples of combat from antiquity are also given, not for the sake of developing a historical narrative, but merely to illustrate a point. His examples are broad and relative to many personality types may enjoy the reading as Walzer references Statesmen, Soldiers, Philosophers, and Theologians. The objective of the book is not to explain morality from the ground up. If he were to make that attempt, it would require a separate book on that particular topic alone. Walzer claims the main intent is one of practical morality. Practical morality in the sense that the book analyzes the moral justifications, judgments, doctrines, and decisions people have made during war times from historical settings to the present day the book was written.

In the second chapter of Just and Unjust Wars, Michael Walzer describes war as a moral dilemma especially relating to Jus ad Bellum, the just cause of war and Jus in Bello, justice in war. Walzer identifies the initiation of war as a crime, borrowing from the philosophy of Karl Von Clausewitz because of the calamity and death it brings, and sometimes without moral considerations. Particularly, Walzer believes war can have a just cause as well as be fought justly. He also believes war can have a just cause, yet fought in an unjust manner. He can also accept as a fact that war can have an unjust cause, yet the Soldiers themselves can still fight justly according to rules of engagement and national agreements. This is significant and contrary to Jeff McMahan’s position that there is no distinction between just cause and just fighting in war because, at its base level, all killing in war is indifferent to the killing by humans in an individual difference.

The difference in context between these two authors is especially pleasing. While Michael Walzer uses figures such as Von Clausewitz to enhance his argument, Jeff McMahan uses Ludwig Wittgenstein. At first, it seems as if McMahan is admiring Wittgentsteing for his intelligence, nut instead McMahan uses Wittgenstein’s ambition to participate in the business of killing while serving in an unjust war as an example of our depraved nature. McMahan raises the character of Wittgenstein so high; that if a brilliant man such as Wittgenstein is willing to kill people in an unjust war, then there is no hope for anyone else.

Jeff McMahan does make a fair assessment of Michael Walzer anytime he references his writing from Just and Unjust Wars. McMahan acknowledges the different views between himself and Walzer. For example, McMahan makes clear mention of Walzer’s views of the two principles of ad Bellum and in Bello and how Soldiers can fight morally justly or unjust regardless of the war itself having a just or unjust cause. McMahan also makes a fair assessment of Walzer’s moral equality of Soldiers. This means that regardless of whether the war has a just or unjust cause, in other words, regardless of the legal status of the war; the moral character of the Soldiers fighting must remain morally independent of the character of the unjust war. The combatants must on all sides have equal rights during the war in relation to morality and regulations, and if abided then all combatants have an equal right to kill only enemy combatants according to Walzer.

Bibliographical Resource

If there was only one bibliographic resource to suggest on the topic of JWT, Michael Farrell’s Modern Just War Theory: A Guide to Research, Scarecrow Press, 2013. ProQuest Ebook Central may very well be the all in one go-to source for an extensive research project model. Farrell’s book may serve as a guide from students to scholars on a multitude of topics revolving around JWT. Contrasting from Jeff McMahan and Michael Walzer, Michael Farrell focuses his research mostly on the twentieth century and the beginning of the twenty-first. Farrell evaluates Christian and secular sources appealing to anyone studying from various backgrounds such as; students, scholars, theologians, philosophers, soldiers, and politicians. Instead of focusing on a specific subject, Farrell surveys several key topics that may expand the reader’s knowledge of JWT; for example, in addition to JWT readers will learn about international law, pacifism, realism, and cosmopolitanism to name a few.

Farrell’s introduction is very direct and to the point. Wasting no time he makes clear to the reader his exact intent and what the reader can expect to gain from his material and the promise of disclosing research methods revealed later in the book for the reader to continue research beyond the book. In chapter one Farrell defines all terms necessary to understand the just war doctrine or the ethics of war such as; Jus ad Bellum, Jus in Bello, Jus post-Bello, and jus ante Bellum which refers to all the actions and diplomacy attempted prior to the hostile breakout of war. His definitions on the principle revolving around the bellum’s and bello’s are insightful,  concise, and comprehendible. Farrell explains additional just war doctrines not usually brought up in other popular sources such as; the doctrine of double effect, humanitarian warfare, asymmetrical warfare, pacifism, and nuclear pacifism, realism, natural law, holy war, crusade, total war, supreme emergency, and nuclear deterrence.

In chapter two Farrell gives a comprehensive summary of the three most cited books of the twentieth and twenty-first century on just war theory. In chapter three he explains the specifics and arrangement of his annotated bibliography of chapter four. In chapter three Farrell also shares with the reader his methods of research and suggestions several different strategies of discovering different sources relevant to just war and ethics of war. Chapter four is the annotated bibliography of dozens of sources all with its own specific concentration regarding JWT. This book is a necessity for anyone earnestly interested in researching JWT.


One of the greatest contemporary philosophical issues from history to the present has been whether a war can be just; which has come to be known as just war theory, (JWT). From history to the present; from theologians to philosophers, politicians, and professional researchers; all have made their attempts to answer the most fundamental questions regarding what constitutes a just war. The attempts from past great thinkers have developed and left behind great western doctrine which has reached an international level. They have also inspired many modern thinkers who have also contributed to the modern development of just war theory. Some of the developers of just war theory were inspired by divine literature, yet they managed to have the wisdom to articulate their thoughts in a way where anyone regardless of spiritual foundations or a lack thereof can understand and appreciate as valued writings. The foundational writings of just war theory from the early western developers are so astute, that it has become merely impossible for modern contributors of just war theory to ignore and neither should be ignored. Modern writers of JWT have become just as important as the early developers. The only matter remaining unfortunate is that war will not end, and to that end neither will just war theory.

Work Cited

Mattox, John Mark. Saint Augustine and the Theory of Just War, Bloomsbury Publishing Plc,

  1. ProQuest Ebook Central,

Aquinas, Thomas. Summa Theologica. Article 1. Question 40. Christian Classics Ethereal

Library. Web. 14 Jul 2019.

Reichberg, Gregory M. “Thomas Aquinas between Just War and Pacifism.” Journal of Religious

Ethics, vol. 38, no. 2, June 2010, pp. 219–241. EBSCOhost, doi:10.1111/j.1467-9795.2010.00427.x

McMahan, Jeff. Killing in War, Oxford University Press USA – OSO, 2009. ProQuest Ebook


Walzer, Michael. Just and Unjust Wars : a Moral Argument with Historical Illustrations.

2nd ed. New York: Basic Books, 1992. Print

Farrell, Michael. Modern Just War Theory : A Guide to Research, Scarecrow Press, 2013.

ProQuest Ebook Central,

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