About Just War Theory

Legitimacy of war is a topic that has always gained my interest. To really understand it though you have to look back at the very start from Saint Thomas Aquinas to modern day Walzer and then; even further.

Intro to Just War Theory

War is usually defined as a contest of violence between two or more belligerent states. Clausewitz’s popular definition of War being a continuation of politics, with the implication of force[1], the fundamental legitimacy of war is apparent. With the Modern Age however, there is the appearance of a new legacy within wars, defined by Max Weber as a “monopoly of legitimate violence”[2] through which belligerent states control their political violence within the bounds of their personal jurisdictions.[3] The traditional themes of just and unjust wars as explained by Weber of jus ad bellum and jus in bello, idyllically explain the means for a justified war and the parameters in which they are fought[4].  Legitimacy of war is reliant on this “Just War” theory. The theory, modernized by Weber and Walzer, originally formulated in Saint Thomas Aquinas’s work, Summa Theologica in the 15th century, usually recognizes “Old Wars” and disregards the 20th and 21st century. Old wars were generally conventional in matter, unlike modern warfare which has shifted from this to an asymmetrical equivalent.


Jus ad bellum & Jus in Bello

International Law dictates two distinct branches and ways of looking at war. These two branches are Jus ad bellum and Jus in bello. Jus ad bellum or justice of war, is about the reason the nation is fighting the war. The second, Jus in bello or justice in war, looks at the means they adopt in the actual fighting of the war. [1] In just war theory, there is also a third aspect of Jus post bellum, which relates to the cessation of war and the just cause for termination of conflict[i].  Jus ad bellum, has a basis of debated criteria to deem a belligerents cause as just. Examples usually fit under the category of “resistance of aggression” – being the violation of basic rights by the use of armed forces, i.e. self-defense of others from an aggressive attack, or the protection of innocent people form an aggressive regime. [2] Usually Just War is recognized by several deontological actions, based on a formal declaration of war by a legitimate authority.  Within reasonable intention and regard to proportionality, probability of success and consideration of conflict being the last resort. Just wars are set out as “good wars” that will accomplish their goals and quash the evil aggressors in a way that will not worsen matters and leave the least amount of casualties of all parties involved. [3] The above criteria is based on the Theory of Aggression as laid out by the aforementioned work of Summa Theologica by Saint Thomas Aquinas. [4]

Jus in bello, relates more to the ethical practice of combat itself. Quintessentially, the motives for engaging in war may be just; but the tactical play of war may not be. Alike to Jus ad bellum, Jus in bello follows a loose criteria that explains what tactics are ethical and morally okay in warfare. These include the need for civilian’s safety, with combatants being the only ones engaged in conflict. Attacks on military, political and industrial targets that are involved in the conflict considered as justified. This related to the next element in the criteria that dictates that the use of horrendous weapons is not deemed as justifiable.[5] Horrendous weapons include that of biological or chemical natures and of course include nuclear and atomic weaponry.  The use of tactics such as carpet-bombing and fire bombing also come under this category as well as the previous category due to its association with cities and civilian harming. Leading on from this, if one party utilizes such weaponry, the idea of equal retaliation deemed as unjust. If one side decides to use Weapons of Mass Destruction, the other parties do not have justification, due to the taking the same or proportionally similar action. This construct also relates to the treatment of Prisoners Of War (POWS). When an enemy surrenders, he or she gives up their combatant status and therefore must be treated as a civilian, therefore treated humanely and decently.


International Law

By 1977, these parameters became international law, with the additional features of the Geneva Conventions that adhere to the criteria laid out by the Just War theories and in turn, privilege states over non-state actors.[6] By 1949 and the commission of the fourth Geneva Conventions, the International law covered only certain fundamental humanitarian rights.  The certain rules, in which participants should adhere to irrespective on the nature of conflict, prohibit the mistreatment of anyone, anytime, anywhere. This includes “murder, torture, corporal punishment, mutilation, outrages upon personal dignity, the taking of hostages, collective punishment, execution without regular trial and all cruel and degrading treatment[ii] [7].“ The 1949 conventions also cover the topics of wounded and shipwrecked combatants and their treatment, as well as POWS. The transformation of International law in the latter part of the 20th century however has shifted from the wellness and rights of not just the individual but also to the rights of the state. This is fully explained in Michael Walzer’s 1977 publication Just and Unjust Wars and how the circle from Theory to Law has now become commonplace in politics.



Now you have a basic understanding of Just War theory and the understandings of International Law, you can start to analyse warfare both classical and contemporary. However, it is always important to remember that warfare is ever-evolving along with laws and theory. For instance modern warfare is leaning evermore asymmetrical making just war theory and its moral and ethical compass, almost redundant.


Most importantly: What do you think?







Just War Theory

[1] Clausewitz, Carl von, Michael Howard, Peter Paret, and Bernard Brodie. 1984. On war. Princeton, N.J.: Princeton University Press.

[2] Weber, Max, and A. M. Henderson. Max Weber: the theory of social and economic organization. Mansfield Centre, CT: Martino Publishing, 2012.

[3] http://www.e-ir.info/2008/07/26/the-legitimacy-of-war-today/

[4]   http://usacac.army.mil/CAC2/MilitaryReview/Archives/English/MilitaryReview_20121031_art004.pdf

Jus ad bellum & Jus in Bello

[1] Walzer, Michael. Just and unjust wars: a moral argument with historical illustrations. New York: Basic Books, 2015.

[2] Walzer, Michael. Just and unjust wars: a moral argument with historical illustrations. New York: Basic Books, 2015.

[3] Rasor, Paul, “Prophetic Nonviolence: Toward a Unitarian Universalist theology of war and peace,”

[4] Walzer, Michael. Just and unjust wars: a moral argument with historical illustrations. New York: Basic Books, 2015.p61

[5] Rasor, Paul, “Prophetic Nonviolence: Toward a Unitarian Universalist theology of war and peace,”

[6] Walzer, Michael. Just and unjust wars: a moral argument with historical illustrations. New York: Basic Books, 1977.

[7] https://www.icrc.org/eng/assets/files/publications/icrc-002-0368.pdf

[i] In this section however, acknowledging the third aspect is key yet it is not an integral part of my argument, hence I regard this third part of just war theory as a mute point.

[ii] As mentioned in the following parts and articles of the Geneva Conventions: I-IV, 3/I-II, 12/III, 13/IV, 32, 34/P.I, 75/P.II, 4, 6. The roman numerals refer to the article and part mentioned and the P in regards to later added conventions in 1977.

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