In discussions with my NCS girls, I have been considering the differences between Michael Walzer's formulation of just war theory and the medieval Catholic tradition. (I will be posting several comments on this issue.) Just and Unjust Wars, note, at no point in the text marches through the classic Catechism criteria of the just war - just authority, just cause, just intent, just means, likelihood of success, and last resort (this is something that sometimes drives teachers of courses on just war theory like me crazy, relying on Just and Unjust Wars as a comprehensive textbook rather than a sustained essay). Why not? Because it is significantly different from classical Catholic just war theology - in ways that might perhaps surprise many who believe that Walzer essentially revived it.
One important clue is found early on in Just and Unjust Wars. Walzer identifies the specific moral problem war as being, he says, a "form of tyranny." (p.29) War is hell, he says, whenever men "are forced to fight, whenever the limit of consent is breached." (p. 28) The essential crime of war, therefore, is that war, almost all of the time, forces people to fight (and noncombatants to be coerced) in ways that breach their consent to take part in this social activity. We can add, too (I believe consistent with Walzer), that there is a moral crime - a violation of justice - by the party that is the aggressor (however that is specifically defined), but there is a closely related moral tragedy insofar as the party resisting aggression must likewise engage in acts of coercion by which to defend itself and its moral rights. But the underlying point is that the injustice arises from the lack of consent, from coercion, from tyranny. Indeed, Walzer emphasizes this point by offering examples of wars that "are not hell ... the first and most obvious example is the competitive struggle of aristocratic young men, a tournament on a larger scale and with no presiding officer in the stands." (p.25) These wars, he says, are not unjust even if they appear, as they might to many of us, to be young men throwing their lives away - what John Ruskin described as "beautiful - though it may be fatal - play." (p. 25)
By describing the essential moral problem of war as being lack of consent, Walzer has firmly aligned his theory of just war with modernity's emphasis of liberty over the earlier medieval values of hierarchy and status. The great importance of Walzer's formulation of the moral foundation for just war theory is that it makes just war theory a branch, in part, of rights and liberties, a branch of Enlightenment morality. This has the great virtue of both hooking it into modernity as well as making it part of modern secular morality. After all, it must be recalled that before Walzer, the just war tradition was really regarded as a mere historical relic of medieval Catholic theology - ignored in theory and practice of ethics, relegated to the backwaters of Catholic thought. (See, e.g., Christopher Lynch, The Triumph of Just-War Theory, Weekly Standard, November 3, 2003.) In the United States, at least (the situation is quite different in European intellectual thought), thanks to Walzer, no one can debate the ethics of war without at least acknowledging the terms of just war theory - and that is so because of his embedding it firmly as a part of the secular ethics of modernity.
Nevertheless, this is not, it seems to me, at all how traditional Catholic theology would conceive of the essential problem of war. Catholic theology would acknowledge the coercive and tyrannical nature of war, yes, but it would not do so by championing consent as the test of morality or even justice. The granting of consent, even when it is real, is not enough to absolve war of its immorality or even injustice, on the Catholic view - Ruskin and the Victorian Romantics were wrong to believe that the killing of human beings, even with consent, can ever be a merely beautiful game. The reason, of course, for Catholicism, is that morality, and even justice, do not stop with relations between human beings, but incorporate relations with God, and therefore even things to which one consents with one's fellows might still be a sin against God, the sin of wagering one's own or a fellow's life without justification.
But of course, this version of just war theory is genuinely theological, a theory of sin and God, and not secular or even very modern. (One could, to be sure, elaborate a secular theory with the same concern - along the lines of John Stuart Mill's arguments against selling oneself into slavery - a secular argument framed along the limits of consent or perhaps the limits of rationality; at some point, however, these supposedly liberal arguments start to look so transcendental in the deployment of such concepts as "rationality" that they begin to look distinctly theological, cf. most of Dworkin.) The point, however, is that Walzer's aim is to embed the tradition of the just war within a secular, Enlightenment morality, and that morality is founded around liberty and equality; libertas locates the theory around consent and coercion, while egalite locates the theory around the essential moral equality of soldiers on each side. If the most traditional form of Catholic just war theory makes the crime of war a sin, then Walzer makes it a matter of a secular morality to which all, at least in theory, can subscribe.