Unit 5: Justice

Contemporary Just War Theory

Femi Omotoyinbo

Femi Omotoyinbo researches on war ethics at the School of History, Anthropology, Philosophy and Politics (SHAPP), Queen’s University, Belfast, United Kingdom. His research interest broadly cuts across applied ethics, and specifically just war theory, moral responsibility, public international law, and African Philosophy. He has taught various topics in ethics, like racism, abortion, animal ethics and global justice, and courses on philosophy of law, problems of philosophy, and African philosophy. With constant innovations and profits from weapons of war and the incessant conflicts across the globe, this chapter from Femi is useful to have a grasp of thoughts and theories that define the nature of war. War is a fixed feature of this world, and this chapter is useful not only to ethically appraise the current situations but also to analyse potential future developments in war. Femi can be contacted via emails: fomotoyinbo01@qub.ac.uk or Jesusphilosopher@live.com.


The fall of Kabul was and remains a big issue of concern that somewhat attracted various critical thoughts about wars. To some people, there is no better way to end the war because war is simply evil in all of its ramifications. Those who hold these reactions are realists. Some people think that the way the war ended in Afghanistan reflects that we should probably not have had the war at all. People with these thoughts are pacifists.

Now, between realists and pacifists are the thoughts that war is intrinsically bad, yet there are duties for participants in a war that could make war less harmful if they are effectively handled. These thoughts constitute what is called just war theory. Therefore, in this piece, we are having an introduction into just war theory in its contemporary analytical forms, its schools of thought, the various conditions or principles of the three focal areas of just war theory and finally we shall highlight some developing areas of further thoughts within just war theory.

Contemporary Just War Theory as Applied Ethics

A brief clarification before continuing is that there is historical or classical just war theory that differs from contemporary just war theory. The former often cuts across the works of scholars like Cicero, St. Augustine, Gratian, Thucydides, Aquinas, Cajetan, Vitoria, Suárez among others. The works of these scholars may arguably not count as part of contemporary just war theory because the methods are comparative and descriptive in their thoughts about wars, particularly those in the Old Testament. Contemporary just war theory is normative, which involves an analytical approach to appraising wars beyond the biblical ones. Thus, further mention of ‘just war theory’ in this discourse is a reference to contemporary just war theory which is a subset of war ethics under the broad pedagogic umbrella of applied ethics.

Brian Orend (2007, p. 571) defines just war theory as “a coherent set of concepts and values designed to enable systematic and principled moral judgement in war time” The concepts and values are poised to minimising unjust suffering in war, especially for (innocent) civilians, right from the start of the war (ad bellum), during the war (in bello), and after the war (post bellum).

Contemporary just war theory arguably starts from Michael Walzer’s seminal book, Just and Unjust Wars and continues with various reactive arguments and counterarguments from some contemporary just war theorists like Jeff McMahan, Henry Shue, Cécile Fabre, Seth Lazar, Yitzhak Benbaji, David Rodin, Helen Frowe, and Susanne Burri. Just war theory aims to ensure justice through these three facets of war by ensuring that those involved in wars are responsible for their actions (Walzer 1977, p. 288). Now, based on their claims and counterclaims, we can roughly categorise contemporary just war theorists into two schools of thought: Traditionalists and Revisionists. We cannot have an exhaustive outline of their differences here, but the main difference concerns the applicability of the principles in just war theory. For the traditionalists, the rights and duties during a war (i.e., in bello context) are the same for all combatants whether just or unjust. This is called the symmetry thesis and it faces rejection through the asymmetry thesis from the revisionists. Also, traditionalists support the independence thesis that rights and duties during a war are not depending on the justice of resorting to the war. For the revisionists, the converse holds, this is the dependence thesis (Rodin and Shue 2008, pp. 2-3). Nevertheless, both traditionalists and revisionists agree that combatants should not deliberately harm non-combatants.

Focal Areas in Contemporary Just War Theory

Here we will be considering the three focal areas of war in just war theory as briefly mentioned above, i.e., Jus ad bellum, Jus in bello and Jus post bellum.

Jus ad bellum (Justice before the war)

Jus ad bellum is etymologically of Latin origin meaning ‘right to war’. It is about the conditions that must obtain to determine whether a resort to war will be just or unjust. The conditions are to answer the question: ‘how do we know that it is right to embark on certain wars?’ These conditions (including those of jus in bello and jus post bellum) are sourced from various thoughts and arguments across traditional and contemporary just war theories. Here are seven of such conditions under jus ad bellum (Frowe, 2011, 52-66):

  1. Just cause: This is about having appropriate reasons to go into war and such reasons could be self-defence, protection of the sovereignty of a state, especially in terms of aggression, unjust occupation, self-determination.
  2. Proportionality: The question here is whether the warfare would be commensurate or match with the actions or activities that trigger the war. For example, it may be unproportionate if a State responds to demolishing a water reservoir by another State by destroying some social facilities and taking the workers hostage.
  3. Reasonable chance of success: The concern here is the likelihood of the war bringing about the desired or desirable just end. Like the return of Afghanistan to the Taliban, it is important to know if the war will end up with the injustice it seeks to correct.
  4. Legitimate authority: In practice, only the head(s) of government has the legitimate authority to order or motivate war against another state or sometimes some non-state aggressors.
  5. Right intention: This concerns the moral side of the cause, which is probably best interpreted as the motives behind the reasons. For example, a reason for war may be to depose a despotic ruler that consistently breaches human rights, but it would count as unjust if the underlying motive is actually to create a state of chaos and gain express access to the resources of the State.
  6. Last resort: Here, the point is that the war should be the last option to consider after the state intending to war have exhausted other options to respond to the provocative situations. Such options could include diplomatic talks, and if applicable, employing judicial options within the international community (e.g., the International Court of Justice (ICJ) or the international human rights court).
  7. Public declaration of war: The last among the conditions for just ad bellum is that the intention to go for war, after the other conditions have been granted, should be made public. There should be no covert war or some sort of secret sabotage or conflict. Perhaps a reason for the public declaration is for the international community to be aware of the war and be able to adjudge the justness of war or to know how to intervene immediately or later on in the future.

Jus in bello (Justice during the war)

Jus in bello is of Latin origin meaning ‘justice during the war’. It is about the conditions that must obtain to adjudge if an ongoing war is just or unjust. As hinted in the dependence/independence theses above, there are contentions about the distinction between jus ad bellum and jus in bello conditions. To some just war theorists, there is no reason for such distinction because the conditions that apply for resort to war are also applicable for conducts during the war (McMahan 2008; Frowe 2018, pp. 42-43). Nonetheless, the rules guiding conducts in war, especially on the nature of permitted weapons, treatment of prisoners of war (POWs) are in international legal conventions like The Hague 1899 and 1907 Conventions and the 1948 Geneva Conventions and its 1977 Protocols. As we shall notice most of the conditions of jus in bello are “prohibitions and restraints in war” (Bailey 1972) ensure fighting well (Walzer 1977, p. 127), especially to guide against unjustified attacks on civilians.

Below are four main conditions of jus in bello:

  1. Qualifying as Combatants: An important point in just war theory is that warfare is normally only for the combatants and there is the need to separate combatants from non-combatants. But what makes a combatant qua combatant? Recall that some of the conditions of jus in bello are already part of international law. Thus, according to the 1949 Geneva Conventions, someone counts as a combatant if:S/he is part of an organised group that has a clear chain of command.
    S/he has an identifiable uniform as a mark of difference from civilians, and sometimes combatants from another chain of command.
    S/he bears arms publicly.
    S/he follows the rules governing conducts in war as enshrined in the Conventions.
  2. Identifying Legitimate Attacks: As a condition of jus in bello, it is required that combatants identify those who are liable to justified attack and those who are not. According to the 1949 Geneva Convention, combatants must avoid intentional attacks on non-combatants either in terms of hostage-taking, torture or killing. Also, combatants who surrender or are incapacitated to fight may count as POWs but they no longer count as legitimate targets. Generally, civilians and civilian objects, such as hospitals, schools etc are not legitimate military targets, such attack is considered criminal. In fact, some domestic legislation contentiously states that a munition factory is a military object that may be attacked but it extends the protection of civilians to include munition workers despite their significant contributions to war (UK Ministry of Defence, 2.5.2, 2004, p. 24). However, there are cases where illegitimate targets may be attacked with little or no consequence depending on the situation. One notable principle that applies in such a situation is called the doctrine of double effect (DDE) which contentiously suggests that sometimes innocent victims may be unintended but foreseen targets of an attack. In military terms, the unfortunate victims may be considered as collateral damage.
  3. Legitimate Tactics: This condition links with the previous one. The condition is that although we have identified those who are liable to legitimate attacks, this is not a sanction for indiscriminate attacks on those ‘deserving’ such attacks. There are acceptable and unacceptable means of attacking legitimate attacks. To consider a tactic as legitimate we should be able to identify whether a) if the attack is necessary to achieve the military objective. For example, destroying a military airbase may be unnecessary if bombing a bridge could help in achieving the same military goal. b) ‘Proportionality’ is also an important element of legitimate military tactics. Proportionality as Helen Frowe (2011/2016, p. 112) rightly puts it is that “the harm that one inflicts must be proportionate to the good that is protected, and must be the least harmful means available of achieving the good.” For example, bombing some factories that produce war materials for the enemy combatants may be proportionate to quell a threat of aggression rather than killing the enemy combatants. Part of the two sub-conditions under legitimate tactics include the nature of the weapons to be employed. Biological, nuclear and chemical weapons are often prohibited in the international legal conventions on war. For example, the three declarations of the first Hague Convention (1899) respectively forbids the discharge of projectiles and explosives from balloons (p. 220); the use of ‘asphyxiating or deleterious’ gases as weapons and expanding bullets (Scott 1915, pp. 225 & 227).
  4. The final condition to consider under jus in bello is the treatment of the prisoners of war (POWs). POWs may include combatants who were injured and thereby incapacitated to fight, or those who were captured or those who voluntarily surrender. This is a recent concern in the war between Russia and Ukraine. These persons can no longer be treated as (enemy) combatants, they should not be punished, harassed or compelled to function as slaves or labourers because of their involvement in the war. POWs are only punishable for whatever offence they commit during their status as POWs. The treatment of POWs is to be vice versa between the warring parties and such treatment tend to be a good ground for jus post bellum.

Jus post bellum (Justice after the war)

Jus post bellum is etymologically of Latin origin meaning ‘justice after war’. It is about conditions that should be in place to end a war and what follows in a just way. According to Larry May (2012, p.1-21), there are “six [interwoven] normative principles of jus post bellum” which are: “rebuilding, retribution, reconciliation, restitution, and reparation, as well as proportionality.” There are views among just war theorists that conditions of jus post bellum are linked with jus ad bellum in such a way that considerations should be given to the post bellum conditions even while war is at the ad bellum stage. Before briefly considering these conditions, it is informative to mention an interesting contention whether the conditions of post bellum should include ‘punishment’. There is the argument that Jus post bellum is forward-looking to restore peace in contrast to punishment which is backwards-looking: revisiting the past to inflict harm on wrongdoers (Lazar 2012, p.220; Fabre 2018, p. 508). Some just war theorists think that the exclusion of punishment in the process of jus post bellum is tantamount to a flagrant disrespect for the suffering of the victims (Orend 2007, p. 580). Meanwhile, we shall not delve into the arguments here but briefly consider the six conditions of jus post bellum - since one of them entails ‘punishment’.


  1. Rebuilding: This is the effort of restoring destroyed institutions, structures and facilities that are significant for afterwar peacebuilding.
  2. Retribution: This is the condition concerning paying back aggressors or unjust contributors to war. Retribution as a condition does not only entail punishment but it concerns the measurement of the punishment to be met out to unjust aggressors.
  3. Reconciliation: A very clear explanation on reconciliation is “ a process of returning previously warring parties to a point not only where they do not engage in violence toward each other but also where there is sufficient trust so that a robust and just peace can be attained – and where a just peace means that human rights are protected.” (May 2012, p. 86).
  4. Restitution: During the war, it is likely that some properties or resources that rightfully belong to certain persons may be lost or taken away from them. Looting of resources is often a characteristic of war. Thus, restitution, as a post bellum condition is about returning the resources or properties to their owners.
  5. Reparation: This is like another side of the coin for restitution because it is also about restoration but here it is about restoring damaged things during a war back to good condition. Classic works in contemporary just war theory suggest that reparation is mainly about wrongful harm from war, and it is usually a post-war attempt to redress injustice to war victims (Walzer 1977, Orend 2006, McMahan 2009).
  6. Proportionality: You will recall that under the conditions of jus ad bellum and jus in bello we have ‘proportionality’ and it was about whether the act of war will be commensurate or match with the actions or activities that trigger the war. Under post bellum, the case is somewhat different. Here ‘proportionality’ is to ensure that efforts to establish peace do not cause more harm than good to the population concerned (May 2012, p. 225). A further explanation is that post bellum proportionality is useful to restrict excessive impositions by the victors on the victims. For example, if there would be an imposition of fines on defeated aggressors it should not be excessive to the detriment of their survival.

So far, we have seen some of the trends of thoughts that constitute just war theory. However, this is obviously a scratch on the surface of the various arguments and counter-arguments that characterise contemporary just war theory. But before concluding it all, it is worthwhile to consider some thoughts/theories that are gaining attention within contemporary just war theory.

Further Thoughts in Contemporary Just War Theory

To conclude this piece, here are a few topics that are fast gaining attention in contemporary just war theory.

Just War Theory and Feminism

This is broadly about feminist perspectives on war. One of the approaches is the presentation of feminism as another alternative reaction to war. This approach suggests that feminism could provoke a more empathetic approach to thoughts and practices in war than what is currently obtained through the extant principles of just war theory (Peach 1994, pp. 152-172). A somewhat similar thought is that there should be a feminist reinterpretation of just war theory which would further give some normative strength to just war theory (Sjoberg 2008, pp. 1-18).

Artificial Intelligence and Just War Theory

Some of the thoughts in the of artificial intelligence concern what is at stake with the use of autonomous weapons, especially with a legal focus on obligations, human liability/culpability and the significance of the application of autonomous weapons for military conduct and justice in war (Pagallo 2011, pp. 307-323). There are also reflections on the application of artificial intelligence in war and the possible moral/legal and political implications for future warfare (Timothy 2020, Omotoyinbo, 2022).

Just War Theory and Climate Change

With the increasing focus on climate change, it is interesting to note any connection between just war theory and climate change. An interesting connection is the application of the conditions of jus ad bellum to assess the military approach to climate change by the United Nations Security Council (Van der Linden 2019, pp. 117-136). Another thought in this area is the use of a just war framework to demonstrate that geoengineering, as a response to climate change may be helpful to some parts of the world but the stance of the international community, probably the well-off countries, to such option seems lethargic (Hedahl and Fruh 2019).

War and Covid19

This is a recently developing area within just war theory, especially since the discovery of the pandemic is relatively recent as well. A known thought here is about how the capitalist approach to arms trade has caused a significant distraction and lack of enough funds to tackle the spread of covid19 at the onset of the pandemic. This thought could be expanded to include a comparison between governments’ reactive approach to covid19 compare to the reactive approach of supplying weapons to earn profits even if the conflicts are unjust. The link to this interesting thought from Andrew Feinstein will be included in the Bibliographical section below.

Suggested Readings/Videos

Feinstein, A., “How Military Spending Affects the Corona Virus Crisis” https://www.youtube.com/watch?v=sK8PIl3kG4Q (accessed on Friday 12th November, 2021).

Lazar, S. and Frowe, H. (eds) (2018) The Oxford Handbook of Ethics of War. Oxford: Oxford University Press.

McMahan, A., “What Rights May We Defend by Means of War?” https://www.youtube.com/watch?v=iEKWJ73Nd94 (accessed on Friday 12th November, 2021).

Walzer, M. 1977/2006. Just and Unjust Wars: A moral argument with historical illustrations (4th edtn), New York: Basic Books.

Walzer, M., “on Terrorism and Just War” https://www.ias.edu/ideas/2007/walzer-terrorism-just-war (accessed on Friday 12th November, 2021).

Bibliographical Notes

1949 Geneva Conventions, https://www.icrc.org/en/doc/assets/files/publications/icrc-002-0173.pdf (assessed on Friday 12th November, 2021)

Bailey, S.D. (1972) Prohibitions and Restraints in War, London: Oxford University Press.

Fabre, C., (2018) War’s Aftermath and the Ethics of War in Lazar, S. and Frowe, H. (eds) The Oxford Handbook of Ethics of War. Oxford: Oxford University Press pp. 507-518.

Frowe H., (2018) “The Just War Framework” in Lazar, S. and Frowe, H. (eds) The Oxford Handbook of Ethics of War. Oxford: Oxford University Press pp. 41-58.

Frowe, H., (2011) The Ethics of War and Peace: Introduction, Oxford: Routledge.

Hedahl M., and Fruh, K., (2019) Climate change is Unjust War – Journal of Philosophy 57(3).

Lazar, S., (2012) Skepticism about Jus Post Bellum in May, L., and Forcehimes, A.T., (eds) Morality and Jus Post Bellum, and International Law. Cambridge University Press: Cambridge.

May, L., (2012) After war ends: A philosophical perspective. New York: Cambridge University Press.

McMahan, J. (2009) Killing in War, Oxford: Oxford University Press.

McMahan, J., (2008) The Morality of War and the Law of War, in Rodin D. and Shue H. (eds) Just and Unjust Warriors: The Moral and Legal Status of Soldiers. Oxford: Oxford University Press, pp. 19-43.

Omotoyinbo, F.R., (2022) Smart Soldiers: Towards A More Ethical Warfare, AI & Society, pp. 1-7.

Orend, B., (2007) The Perspective of a Just War Theorist. Leiden Journal of International Law 20:3, pp. 571-591.

Orend, B., (2006) The Morality of War, Ontario: Broadview Press.

Pagallo U., (2011) Robots of Just war: a Legal Perspective, Philosophy and Technology 24(3) pp. 307-323.

Peach, L. J., (1994) An Alternative to Pacifism? Feminism and Just-war theory, Hypatia 9(2) pp. 152-172.

Rodin, D. and Shue H., (2008) Introduction, in Rodin D. and Shue H. (eds) Just and Unjust Warriors: The Moral and Legal Status of Soldiers. Oxford: Oxford University Press, pp. 19-43.

Scott, J.B., (1915) The Hague Conventions and Declarations of 1889 and 1907. New York: Oxford University Press.

Sjoberg, L., (2008) Why just war needs feminism now more than ever – International Politics 45 (1) pp. 1-18.

Timothy J. Demy, (2020) “Something Old, Something New” – Reflections on AI and the Just War Tradition, Artificial Intelligence and Global Security, Emerald Publishing.

UK, Ministry of Defence, (2004) Manual of the Law of Armed Conflict, Oxford: Oxford University Press.

Van der Linden, H., (2019) Climate change mitigation and the UN Security Council: A Just war Analysis. Pacifism, Politics and Feminism, pp. 117-136.

Walzer, M., (1977/2006) Just and Unjust Wars: A moral argument with historical illustrations (4th Ed), New York: Basic Books.


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