For my Christian Ethics (ET 501) course at Fuller Theological Seminary, we have been reading Glen Stassen and David Gushee, Kingdom Ethics (IVP Academic, 2003). In their chapter on three different Christian positions on the (im)permissibility of violence, they provide the following eight rules of Just War theory. These are rules by which the theory proposes a person may evaluate whether or not engaging in war in some particular circumstances would be just or unjust, permitted or impermissible.
There are seven rules about jus ad bellum, justice in deciding to go to war, and one rule about jus in bello, justice in war itself. The rules are grounded in the prior conviction and commitment that to kill is a grave evil and may only be done in certain circumstances and for the right reason. Because of this we may understand Just War theory as a means of upholding Jesus' decidedly non-violent ethic, since it allows for recourse to violence only in very highly specified circumstances. It becomes obvious that on Just War theory, violence is only justifiable when it means preventing much worse violence for as minimal a cost as possible.
1. Just cause. The causes that can override the presumption against killing are stopping the massacre of large numbers of people and stopping the systematic and long-term violation o the human rights of life, liberty and community (p. 159).
2. Just authority. To commit a nation to make a war in which many will die and be maimed is an enormous responsibility. No one can do that without just authority. Constitutional processes must be followed, so the people who will pay with their lives and resources will be represented in the decision (p. 159). Furthermore, the approval of the United Nations or a representative international body or coalition should generally be sought, for two reasons. The cost in resources, wounded and dead will be borne by other nations as well. And nations that decide to go to war often are wrong (p. 160).
3. Last resort. All means of negotiation, conflict resolution and prevention must be exhausted before resorting to war. The logic is clear: what justifies the killing in war is that it is the only way to stop the great evil that provides the just cause. If the evil can be stopped by a nonviolent resort, then there is no just cause for the killing (p. 160).
4. Just intention. The only legitimate intention is to secure a just peace for all involved. Neither revenge nor conquest nor economic gain nor ideological supremacy are justified (quoted at p. 160).
5. Probability of success. It is wrong to enter into a war that will kill many people, depriving them o the right to life, liberty and community, in order to achieve a more important goal, if we will quite surely lose and not achieve that goal, and all those people will die in vain (p. 161).
6. Proportionality of cost. Proportionality requires that the total good achieved by a victory will . . . outweigh the total evil and suffering that the war will cause. No one should prescribe a cure that is worse than the disease (quoted at p. 161).
7. Clear announcement. The government that is about to make war must announce its intention to make war and the conditions for avoiding it. Stipulating the conditions for avoiding war enables the other side to know what it would take to avoid or stop the war (p. 162).
8. The war must be fought by just means (jus in bello). In a pragmatic culture like the United States, a frequent error is to emphasize the justice of the cause but then overlook the requirement that the means of fighting must be just. . . . This criterion of justice in war "forbids direct, intentional attacks on nonmilitary persons" . . . Individuals not actively contributing to the conflict (including POWs and causalities as well as civilian nonparticipants) should be immune from attack (p. 162). Because collateral damage may be inevitable, recourse is made to the principle of double effect: engaging in action which may result in civilian deaths is just so long as the intention is to attack armed combatants, and so long as its cost in lives is proportional to the gain (p. 163).
These days Just War theory makes more sense and is more plausible to me than a more committed pacifism, if only because the stated conditions of just war are so strict as prevent war except precisely in those cases in which pacifism is most implausible. For instance, Just War theory may have permitted intervention in the case of the Rwandan genocide, a case which is very difficult if not impossible for the pacifist to address.
(A small note: the authors write jus ad bello [p. 158] which is grammatically incorrect Latin. The preposition ad takes an accusative object, and the accusative of the neuter noun bellum, war, is bellum and not bello. The authors missed this and the editors missed this, and it is embarrassing. This is why everyone should study Latin, so that they do not make erreurs pénibles such as this. Schopenhauer said you are not educated unless you know Latin and Greek. He was right. See what Bill says here.)