Stanford Encyclopedia of Philosophy http://plato.stanford.edu/entries/war/#2
The following is an excerpt from the above web site for teaching use only.
2. Just War Theory
Just war theory is probably the most influential perspective on the ethics of war and peace. The just war tradition has enjoyed a long and distinguished pedigree, including such notables as Augustine, Aquinas, Grotius, Suarez, Vattel and Vitoria. Hugo Grotius is probably the most comprehensive and formidable classical member of the tradition; James T. Johnson is the authoritative historian of this tradition; and many recognize Michael Walzer as the dean of contemporary just war theorists. Many credit Augustine with the founding of just war theory but this is incomplete. As Johnson notes, in its origins just war theory is a synthesis of classical Greco-Roman, as well as Christian, values. If we have to “name names”, the founders of just war theory are probably the triad of Aristotle, Cicero and Augustine. Many of the rules developed by the just war tradition have since been codified into contemporary international laws governing armed conflict, such as The United Nations Charter and The Hague and Geneva Conventions. The tradition has thus been doubly influential, dominating both moral and legal discourse surrounding war. It sets the tone, and the parameters, for the great debate.
Just war theory can be meaningfully divided into three parts, which in the literature are referred to, for the sake of convenience, in Latin. These parts are: 1) jus ad bellum, which concerns the justice of resorting to war in the first place; 2) jus in bello, which concerns the justice of conduct within war, after it has begun; and 3) jus post bellum, which concerns the justice of peace agreements and the termination phase of war.
2.1 Jus ad bellum
The rules of jus ad bellum are addressed, first and foremost, to heads of state. Since political leaders are the ones who inaugurate wars, setting their armed forces in motion, they are to be held accountable to jus ad bellum principles. If they fail in that responsibility, then they commit war crimes. In the language of the Nuremberg prosecutors, aggressive leaders who launch unjust wars commit “crimes against peace.” What constitutes a just or unjust resort to armed force is disclosed to us by the rules of jus ad bellum. Just war theory contends that, for any resort to war to be justified, a political community, or state, must fulfill each and every one of the following six requirements:
1. Just cause. This is clearly the most important rule; it sets the tone for everything which follows. A state may launch a war only for the right reason. The just causes most frequently mentioned include: self-defense from external attack; the defense of others from such; the protection of innocents from brutal, aggressive regimes; and punishment for a grievous wrongdoing which remains uncorrected. Vitoria suggested that all the just causes be subsumed under the one category of “a wrong received.” Walzer, and most modern just war theorists, speak of the one just cause for resorting to war being the resistance of aggression. Aggression is the use of armed force in violation of someone else's basic rights.
The basic rights of two kinds of entity are involved here: those of states; and those of their individual citizens. International law affirms that states have many rights, notably those to political sovereignty and territorial integrity. It thus affirms that aggression involves the use of armed forces—armies, navies, air forces, marines, missiles—in violation of these rights. Classic cases would be Nazi Germany into Poland in 1939, and Iraq into Kuwait in 1990, wherein the aggressor used its armed forces to invade the territory of the victim, overthrow its government and establish a new regime in its place. Crucially, the commission of aggression causes the aggressor to forfeit its own state rights, thereby permitting violent resistance. An aggressor has no right not to be warred against in defense; indeed, it has the duty to stop its rights-violating aggression.
But why do states have rights? The only respectable answer seems to be that they need these rights to protect their people and to help provide them with the objects of their human rights. As John Locke, and the U.S. Founding Fathers, declared: governments are instituted among people to realize the basic rights of those people. If governments do so, they are legitimate; if not, they have neither right nor reason to exist. This is vital: from the moral point of view, only legitimate governments have rights, including those to go to war. We need a theory of legitimate governance to ground just war theory, and Aquinas perhaps saw this more clearly than any classical member of the tradition. This connection to legitimacy is consistent with the perspective on war offered so far: war, at its heart, is a violent clash over how a territory and its people are to be governed.
Based on international law (see Roth), it seems like there are three basic criteria for a legitimate government. If these conditions are met, the state in question has rights to govern and to be left in peace. They are as follows. First, the state is recognized as legitimate by its own people and by the international community. There is an uncoerced general peace and order within that society, and the state is not shunned as a pariah by the rest of the world. Second, the state avoids violating the rights of other legitimate states. In particular, legitimate governments don't commit aggression against other societies. Finally, legitimate states make every reasonable effort to satisfy the human rights of their own citizens, notably those to life, liberty and subsistence. States failing any of these criteria have no right to govern or to go to war. We can speak of states satisfying these criteria as legitimate, or “minimally just,” political communities.
Why do we need to talk about these rights? First, to give state rights moral legitimacy and to avoid fetishizing state rights for their own sake. Second, to describe what is wrong about aggression and why it justifies war in response. Aggression is so serious because it involves the infliction of physical force in violation of the most elemental entitlements people and their communities have: to survive; to be physically secure; to have enough resources to subsist at all; to live in peace; and to choose for themselves their own lives and societies. Aggression thus attacks the very spine of human civilization itself. This is what makes it permissible to resist with means as severe as war, provided the other jus ad bellum criteria are also met. Third, talk of legitimacy is essential for explaining justice in a civil war, wherein there isn't classical, cross-border aggression between competing countries but, rather, a vicious fight over the one state between rival communities within a formerly united society. The key to discerning morality in such cases revolves around the idea of legitimacy: which, if any, side has minimal justice? Which side is defending—or is seeking to establish—a legitimate political structure in our three-fold sense? That's the side which it is permissible to: a) be part of; or b) if you're an outsider, to support.
How does this conception of just cause impact on the issue of armed humanitarian intervention? This is when a state does not commit cross-border aggression but, for whatever reason, turns savagely against its own people, deploying armed force in a series of massacres against large numbers of its own citizens. Such events happened in Cambodia and Uganda in the 1970s, Rwanda in 1994, Serbia/Kosovo in 1998-9 and in Sudan/Darfur from 2004 to the present. Our definitions allow us to say it's permissible to intervene on behalf of the victims, and to attack with defensive force the rogue regime meting out such death and destruction. Why? There's no logical requirement that aggression can only be committed across borders. Aggression is the use of armed force in violation of someone else's basic rights. That “someone else” might be: a) another person (violent crime); b) another state (international or “external” aggression); or c) many other people within one's own community (domestic or “internal” aggression). The commission of aggression, in any of these forms, causes the aggressor to forfeit its rights. The aggressor has no right not to be resisted with defensive force; indeed, the aggressor has the duty to stop and submit itself to punishment. If the aggressor doesn't stop, it is entirely permissible for its victims to resort to force to protect them—and for anyone else to do likewise in aid of the victims. Usually, in humanitarian intervention, armed aid from the international community is essential for an effective resistance against the aggression, since domestic populations are at a huge disadvantage, and are massively vulnerable, to the violence of their own state.
Terrorists can commit aggression too. There's nothing to the concept which excludes this: they, too, can deploy armed force in violation of someone else's basic rights. When they do so, they forfeit any right not to suffer the consequences of receiving defensive force in response. Indeed, terrorists almost always commit aggression when they act, since terrorism is precisely the use of random violence—especially killing force—against civilians, with the intent of spreading fear throughout a population, hoping this fear will advance a political objective. On 9/11, the al-Qaeda terrorist group clearly used armed force, both to gain control of the planes and then again when using the planes as missiles against the targets in The Pentagon and The World Trade Center. This use of armed force was in violation of America's state rights to political sovereignty and territorial integrity, and to all those people's human rights to life and liberty. The terrorist strikes on 9/11 were aggression—defiantly so, deliberately modeled after Pearl Harbor. As such, they justified the responding attack on the Taliban regime in Afghanistan. The Taliban had sponsored and enabled al-Qaeda's attack, by providing resources, personnel and a safe haven to the terrorist group.
An important issue in just cause is whether, to be justified in going to war, one must wait for the aggression actually to happen, or whether in some instances it is permissible to launch a pre-emptive strike against anticipated aggression. The tradition is severely split on this issue. Vitoria said you must wait, since it would be absurd to “punish someone for an offense they have yet to commit.” Others, like Walzer, strive to define the exceptional criteria, stressing: the seriousness of the anticipated aggression; the kind and quality of evidence required; the speed with which one must decide; and the issue of fairness and the duty to protect one's people. If one knows a terrible attack is coming soon, one owes it to one's people to shift from defense to offense. The best defense, as they say, is a good offense. Why let the aggressor have the upper hand of the first strike? But that's the very issue: can you attack first and not, thereby, yourself become the aggressor? Can striking first still be considered an act of defense from aggression? International law, for its part, sweepingly forbids pre-emptive strikes unless they are clearly authorized in advance by the UN Security Council. These issues, of course, were highlighted in the run-up to the 2003 U.S.-led pre-emptive strike on Iraq. The U.S. still maintains, in its National Security Strategy, the right to strike first as part of its war on terror. Many other countries find this extremely controversial.
2. Right intention. A state must intend to fight the war only for the sake of its just cause. Having the right reason for launching a war is not enough: the actual motivation behind the resort to war must also be morally appropriate. Ulterior motives, such as a power or land grab, or irrational motives, such as revenge or ethnic hatred, are ruled out. The only right intention allowed is to see the just cause for resorting to war secured and consolidated. If another intention crowds in, moral corruption sets in. International law does not include this rule, probably because of the evidentiary difficulties involved in determining a state's intent.
3. Proper authority and public declaration. A state may go to war only if the decision has been made by the appropriate authorities, according to the proper process, and made public, notably to its own citizens and to the enemy state(s). The “appropriate authority” is usually specified in that country's constitution. States failing the requirements of minimal justice lack the legitimacy to go to war.
4. Last Resort. A state may resort to war only if it has exhausted all plausible, peaceful alternatives to resolving the conflict in question, in particular diplomatic negotiation. One wants to make sure something as momentous and serious as war is declared only when it seems the last practical and reasonable shot at effectively resisting aggression.
5. Probability of Success. A state may not resort to war if it can foresee that doing so will have no measurable impact on the situation. The aim here is to block mass violence which is going to be futile. International law does not include this requirement, as it is seen as biased against small, weaker states.
6. Proportionality. A state must, prior to initiating a war, weigh the universal goods expected to result from it, such as securing the just cause, against the universal evils expected to result, notably casualties. Only if the benefits are proportional to, or “worth”, the costs may the war action proceed. (The universal must be stressed, since often in war states only tally their own expected benefits and costs, radically discounting those accruing to the enemy and to any innocent third parties.)
Just war theory insists all six criteria must each be fulfilled for a particular declaration of war to be justified: it's all or no justification, so to speak. Just war theory is thus quite demanding, as of course it should be, given the gravity of its subject matter. It is important to note that the first three of these six rules are what we might call deontological requirements, otherwise known as duty-based requirements or first-principle requirements. For a war to be just, some core duty must be violated: in this case, the duty not to commit aggression. A war in punishment of this violated duty must itself respect further duties: it must be appropriately motivated, and must be publicly declared by (only) the proper authority for doing so. The next three requirements are consequentialist: given that these first principle requirements have been met, we must also consider the expected consequences of launching a war. Thus, just war theory attempts to provide a common sensical combination of both deontology and consequentialism as applied to the issue of war.