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War represents one of humanity’s most profound moral dilemmas. Societies and cultures have therefore had thousands of years to think about how and when it can or should be undertaken. This thinking is captured in the Just War Tradition (JWT). For AI developers, an understanding of war ethics, particularly JWT, is highly relevant. The growing integration of AI into military applications places developers at the forefront of creating tools that influence life-and-death decisions. By engaging with JWT, developers gain essential insights into ethical principles that govern warfare, allowing them to design AI systems that adhere to international norms and moral standards.

 

 

1. What is the Just War Tradition?
The Just War Tradition (JWT) offers a structured framework for assessing whether and how war can ever be ethically justified. Developed over centuries by thinkers such as Augustine, Thomas Aquinas, and Hugo Grotius, this tradition continues to shape moral philosophy and international law. By asking whether there can be rules for war, we engage with the principles of JWT, which divides the ethics of war into three key phases:

This discussion centres on Jus ad Bellum, which outlines the criteria for determining whether going to war is morally defensible in a modern context. See Does war have rules? for the Jus in Bello - the rules in war. Soldiers are not necessarily responsible for the decision to go to war, but they are responsible for its conduct. Very senior military officers may straddle this line, but, as the famous Just War theorist Michael Walzer points out, this gives us a pretty good idea of where that line should be drawn.

While an unjust cause cannot be made better by fighting a war well, one can certainly undermine a just cause by conducting a war badly. Therefore, the ad Bellum and in Bello levels of war are clearly related in a number of ways, but they also remain distinct.

Below we work through the core principles that, when considered together, have a strong influence on whether each side in any conflict are considered just or unjust.

 

 

2. What are the principles of Jus ad Bellum (justice of going to war)

1. Just cause: A just cause is the cornerstone of moral justification for war. The clearest example of a just cause is when a state acts in self-defence due to a direct attack against its people or its territory. This is enshrined in Article 51 of the UN Charter, which affirms the inherent right of self-defence possessed by every state: ‘Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs.’ Thus, an action taken in direct self-defence requires no additional authority to sanction it. Defending a neighbour or an ally or responding to requests to protect the weak against the strong can also be examples of acting in defence.

2. Right intention: Most people would accept that the motivation of an act has a bearing on whether or not it can be judged morally good or bad. While satisfying the just cause criteria can help establish that one is doing the right thing, having the right intention is necessary to ensure that one is doing it for the right reasons. Creating, restoring or keeping a just peace, righting wrongs and protecting the innocent would all clearly qualify as right intentions while seeking to expand one’s territory, enslave or convert others to one’s religion, hatred or revenge would not.

Motivation shapes action and if a conflict is motivated by these last two emotions in particular, it becomes all too easy for the enemy to be regarded as less than an equal. Such a climate makes it far more likely that war crimes and atrocities will be committed. Of course, good intentions are often mixed up with those that are less so and, anyway, how does one really know what motivates a state to act? It would be naive to assume that one can always find a single, pure motivation for an action, particularly in the messy world of international politics. However, this does not diminish the importance of this principle as it recognises that wars fought primarily for the wrong motives will invariably lead to an unjust peace. This, in turn, is likely to sow the seeds for further conflict in the long run.

3. Legitimate authority: Acting in direct self-defence requires no further authority. However, anything that does not fall into this category requires a declaration by a legitimate authority. When an injury has been suffered, the offending party has to be told what it is they have done wrong, and also what it is they can do to restore the situation and therefore prevent war. Some have questioned the continued usefulness of such a declaration, particularly given that one does not actually tend to declare or use the formal language of “war” anymore in public discourse. However, the clear declaration of what has been done wrong before embarking on a conflict, whether it is legally called war or not, is more than purely procedural and remains pertinent if the other side is to have any chance of rectifying the situation or making redress. Demonstrating the way that the Just War principles can become intertwined, it would be very hard to demonstrate that one had reached the point of Last Resort if this declaration had not yet happened.

Article 2(4) of the UN Charter declares: ‘All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.’ Therefore, every UN member state has agreed that everything other than actions taken in immediate self-defence requires the prior authority of the Security Council. However, in practice, the actual power to do this still appears to rest with states or their regional alliances rather than exclusively with the UN. Even here though, states still have legal procedures for committing their armed forces into a conflict and these need to be adhered to before any such deployment can be considered to have legitimate authority. All states have some kind of constitutional mechanism for ensuring that their armed forces can only be legitimately employed under certain conditions. It is arguable that legitimate authority does not have to be state-centric, but it must be possible to at least demonstrate a significant measure of popular support amongst those on whose behalf the activity is being undertaken.

4. Proportionality: While war might be legitimate to right certain wrongs, not all wrongs can legitimise war – one must therefore ask whether the overall harm likely to be caused by the war is less than that ‘caused by the wrong that is being righted’. Is war a proportionate response to the injury received, or not?
Of course, this can be a very subjective criterion to fulfil – after all, what value does one put on something as intangible as national honour? This question demonstrates why this principle cannot be purely a prudential matter, for we must take into account the total cost of the war, not just the cost to ourselves. Clearly, this is an enormously difficult assessment to make in advance of military action, particularly due to the inevitable unintended consequences and knock-on effects that may be impossible to accurately predict. However, the Just War Tradition asks that at least a credible attempt be made to answer this question before committing to the use of force.

5. Reasonable prospects of success: Some people may regard it as noble to die fighting for a hopeless cause. However, even while recognising that war involves at least some degree of evil, most accept that it is unethical to sacrifice life and cause unnecessary pain and suffering if there is not at least a reasonable chance that it will change anything. Clearly, this is a prudential calculation.
Of course, asking this question also means that one must have a clear idea of what success is in this situation. Few people would deny that it is sound strategic planning to ask what war is trying to achieve before embarking upon it. By establishing a clear and realistic objective at the outset, mission creep can be avoided and war can be kept firmly as an instrument of policy rather than its master. Outright victory through the categorical defeat of the other side may not be the definition of success that is required. For example, in 1939 Finland defended itself against the Soviet Union even though it clearly could not win. On the face of it, this would not satisfy the reasonable prospect of success criteria. However, the Finns almost certainly obtained significantly better terms, when they did finally capitulate five months later than they would have achieved if they had not fought at all. Their definition of success therefore was never victory in the normal sense of the word.

6. Last resort: Has every rational nonviolent alternative been tried before armed force is employed? Such alternatives could include diplomacy, international political pressure and economic sanctions, among many other options. Of course, it is always possible to do something that is nonviolent even if it will have absolutely no chance of succeeding, so how does one genuinely know that the point of last resort has been reached? The last resort simply requires that all other practical options that might achieve success have been exhausted before military action is initiated. Given that the context may be very time-sensitive, it may of course be that some options are simply unavailable.

 

3. Can war ever be justified?

The Just War Tradition (and the legal and moral norms that it represents) is not necessarily about providing a set of answers. It is not a formula which somehow generates a successful outcome as long as the right things are put into it. However, it can help to structure decision-making as the factors it asks us to consider should be taken into account before and during any use of armed force. It is more than just a tick-box exercise as each of the principles relate to, and interact with, each other. The more convincing the answers to all of the questions, the more likely one side or the other in a conflict are going to be considered to be on the ‘right’ side, with all of the ensuing implications for domestic and international support. The JWT provides a framework for distinguishing between justifiable military action within an ethical framework, and murder on a massive scale.

Adapted from D Whetham (Ed.), Ethics, Law and Military Operations (Basingstoke: Palgrave Macmillan, 2010).