Edward Feser at "Right Reason" (here and here) has been arguing that the war in Iraq was a just war, but I'm not buying it. Part of it, of course, is that strictly speaking, just war theory doesn't actually talk about 'just wars'; a war, as such, is neither just or not. Rather, just war theory talks about just warring, or, to be even more accurate, about leaders being just even in acts of war. The basic foundation for such a position is expressed well in Aquinas's three requirements: as prince of a city you can be just if you act from legitimate authority, with the proper disposition, toward the right end. All the maxims and criteria are intended as guidelines for what constitutes being just in matters of war. Feser goes through some of these maxims in order to argue that Bush's going to war in Iraq fits the criteria. I will comment on some of these.
(1) Legitimate authority. The only persons who can go to war are those who lead states in such a way that they are responsible for the security of those states. Feser attempts to dismiss the "quibble" that the war was not declared by Congress, on the basis that just war theory is not concerned with the specific mechanisms of authority; but this seems to me to be a very bad argument. Just war theory does not, it is true, dictate how legitimate authority is to be determined; but that's because it respects the facts of authority in each case. The U.S. Constitution splits the authority between Congress (the power to declare war) and the President (who is Commander-in-Chief). As Feser notes, there was a Congressional resolution in favor of the war; it can reasonably be argued that this counts. But this is a long way from saying that the objection is a quibble; on the contrary, it raises a very important point, even though it is not the strongest ground on which to object to the Iraq war.
(2) Just Cause. War can only be fought in defense of a violated right. As Feser notes, this is usually not understood in such a way as to constrain to a merely defensive war. Rather, it extends to any protection of rights under natural law or the law of nations (which is not international law, but that aspect of international law that international law must presuppose). The oppression of the innocent would certainly count. If it isn't a mere excuse. For what matters in just cause is not what cause may be appealed to; what matters is the actual purpose of the action of war. Just cause is a matter of ends (a just cause is that end to which a just action is directed), and what is more, it is a matter of actual ends, not possible ends. Therefore Feser moves far too quickly when he says that it's clear that the war in Iraq meets the criteria of just cause; because all he indicates are things that would certainly be considered just if unadulterated. It is possible to ruin any just end by mixing it with unjust ends. It is not enough for there to be something just to which one appeals in going to war; that something just has to define one's purpose for going to war, without admixture from anything unjust. Thus many opponents of the war are quite willing to say that there were potential just causes for military action to remove Saddam Hussein; what they deny is that we actually went to war with just cause.
(3) Last resort. The other major avenues of resolution (negotiation, mediation, arbitration, sanction, moral suasion, and the like) must be of no avail. Feser is right that a simplistic notion of last resort is clearly unsustainable. But last resort is still a tricky issue; for it isn't clear that the war was a last resort. The last resort, remember, would have to be the last resort with regard to the just cause. But most of the debate prior to the war wasn't about any plausible just causes but about "weapons of mass destruction." The real debates -- about what would be the best way to go about protecting Kuwait from Iraq, or protecting the Kurds from Saddam Hussein, or any other such case, never really happened.
(4) The knowability of the just cause as just. Feser is right that Ryba's argument on this point is simply bizarre. All that's needed for this is good character and a recognition of the principles of justice.
(5) Right intention. This one always bothers me, because in medieval jsut war theory 'right intention' means (more or less) 'right disposition'. What we usually mean is 'intended in the right way'; which is legitimately a concern, but only one of many. Understood in this way it is not a matter of disposing oneself properly to the fulfillment of the end but instead is merely just cause restated.
(6) Right means. In fact, it is questionable whether anyone today uses right means; to engage in right means you cannot (for instance) lie, and you cannot accept, even indirectly, the deaths of innocents as a means to your end. We, on the other hand, institutionalize lying in government agencies and military operations that are in part supposed to do exactly that.
The key issue, and the one that seems missing entirely from Feser's analysis, is that justice with regard to war is very difficult. You can be just in war, but you cannot merely assume that you are just on the basis of a few procedures; it requires continual soul-searching and a serious, complete devotion to moral good. The above is not an argument that Bush was unjust in war; rather, it's that the defense of the just even in just war is not so easy: it is an arduous examination only the just can endure.