According to the Just War tradition a war can only be just if two sets of principles are satisfied. (1) First there is the jus ad bellum. These principles tell us when it is just to start a war. There has to be a good reason or a just cause in order for a war to be morally permissible (self-defense, defense of others, putting a stop to human rights violations). The decision to go to war has to be taken by a legitimate authority. Those who wage war need to be motivated by good intentions (desire to promote a more stable peace). War should not only be a last resort (necessity), it must also offer a reasonable chance of success. Moreover, the good the warring party hopes to obtain should outweigh the evil caused by the war (proportionality). The second set of principles, the jus in bello or the right in the war, focuses on the moral constraints that need to be observed during hostilities. Noncombatants must never be the intentional target of military actions (discrimination), and the military utility of a particular act of war has to outweigh the damage it will cause.
It is clear that combatants, whatever side they are on, have a moral and legal obligation to respect the in hello principles. This is what ethicists call their in bello responsibility. Can combatants be held responsible for participating in an unjust war? Do they, aside from their in hello responsibility, have an ad bellum responsibility? If so, this would mean that combatants have a duty to judge the justice of the war and refuse to participate in an immoral conflict. Those combatants who would not take such an ad bellum responsibility seriously, and simply follow orders, would risk being considered unjust combatants. Anyone who studies the moral and legal reality of warfare will quickly notice that this presumption of military ad bellum responsibility is firmly rejected. (2) At the core of the Just War tradition is the fundamental doctrine of the moral equality of combatants. Basically this doctrine says that the realm of responsibility of combatants on all sides is equally limited to that of the jus in bello. Combatants cannot be held responsible for the just or unjust nature of the war in which they participate. The ad bellum responsibility belongs solely to the political decisionmakers.
Despite its basic role in the normative appreciation of war, the doctrine of moral equality of combatants is not beyond dispute. Even Michael Walzer, who is a strong defender of a strict separation between jus ad bellum and jus in bello, admits that this moral dualism can be somewhat puzzling. (3) It is, after all, far from obvious that the moral status of a combatant in a defensive war is the same as that of a combatant participating in a war of aggression. The former is clearly engaged in a morally legitimate activity (self-defense), whereas the latter is contributing to what most would term a criminal act. So, how can these two be moral equals? Should we not add an ad bellum responsibility for combatants? If, as some philosophers and lawyers argue, we decide to hold soldiers responsible in this regard, wouldn't that stop them from participating in wars of aggression? (4)
The objective of this article is to shed light on this problem by answering two questions: (a) What arguments are there to support the traditional position that limits the responsibility of the military to the jus in bello? and (b) Can combatants ever be blamed for unjust wars, and if so, under what circumstances?
Perhaps the most straightforward reason why the responsibility of the military is limited to the jus in bello has to do with the strict military subordination to political authority. Politicians decide to go to war, whereas the military is expected to execute this decision to the best of its ability. This subordinate role does not, however, reduce the military to a mere political instrument that obeys orders without question. …