Ward Thomas wishes to know where and how the norms governing the international use of force originate, how they are perpetuated, and how they decline. His interesting argument is that they have two lines of descent. One is from a priori moral principles—general statements about right and wrong. Ethical norms take these abstract propositions and apply them in more specific circumstances, as it could be argued that the Hippocratic oath applies general notions about treating others humanely to the peculiar dilemmas faced by physicians. The other source is found in the interests of powerful states; potential rules of conduct do not become and remain operative guides to action unless they are consistent with the perceived well-being of those actors in the international system holding the power to enforce or to flaunt them. If the rules of international life are not consistent with moral principles, it is a misnomer to term them “ethical” norms; if they run athwart the interests of the centers of international power, they will not last. In two extended case studies—one tracing the norm against international assassination and a second, much longer examination of the rise, fall, and subsequent revival of the norm against aerial bombing of cities—Thomas explores the interplay of power and principle that issues in norms. The union is not always a harmonious one, but, as with Dr. Johnson's dog walking upright, the wonder is that it is done at all.

To arrive at this double-barreled normative conception requires confidence that stable resting places do exist at which a rule that derives its moral force from its impartiality among the interests and obligations of all those to whom it applies can also perform the “power-maintenance function” of preserving the position of the holders of great power against their challengers. It is comparatively easy to demonstrate, as is deftly done here, that to contend that the only ethical actions are those that are completely altruistic and self-sacrificing is to establish a standard that practically no action could meet. It is more difficult to argue that anything other than coincidence will allow a rule to serve both one's power needs and one's moral duties, at least for long periods of time. No harm would have been done to this excellent book by a fuller exploration of the Niebuhrian theme that although the two are theoretically incompatible, patient and far-sighted statesmanship may bring them into an uneasy coexistence with some staying power.

The book opens with the famous quote from Clausewitz that moderation and limitations on force are foreign to the theory of war, by which he means that war as such is pure violence directed at the destruction of the enemy (“absolute war”). In saying that Clausewitz is wrong (p. 1), however, Thomas is actually advocating the Clausewitzian alternative of “real war,” under which the political objectives of states allow and may mandate the introduction of various restrictions on the unrestrained ferocity of war in theory, so as to make war a controllable instrument of state policy. This policy stems from diplomatic goals, not moral obligations, though, and if the limitations fail to serve one's diplomacy they will be discarded. Just so, Thomas contends that when “vital” national interests conflict with the general interest of international society in the preservation of a rule of conduct, the national interests may well prevail. The “anarchical society” is always subject to breaking down if great powers calculate that their unshared interests outweigh the common interest in shared institutions and practices, of which limitations on wartime behavior form a prominent example.

When Thomas describes states as “participants in a larger social project defined by common interests” (pp. 21–22), he is not going over to an alternative, non-Clausewitzian theory of war—war as a social relationship, as an effort by an organized group of humans to promote justice and rectify injustice, to bring human society back to a well-ordered condition, and to strenghthen the natural condition among humans and the true object of every war, a more solidly grounded state of peace. His contribution to the Grotian tradition of the “English school” does not fly so high as that, and in remaining on the terra firma of self-interest, he grants that ethical limitations on force will always remain vulnerable to changes—in national objectives, in patterns of international alignment, or in technology—that will cause states, if they can, to throw off self-restraint and move in the direction of destructive “absolute war.” Moreover, “convention-dependent” norms depend on reciprocity, so that if one party (say, one belligerent) abandons them, the other has little reason not to follow suit. Even an alteration in policy that is intended only to modify a norm is difficult for an opponent in the distrustful atmosphere of war to distinguish from abandonment, so that the end result is the same: the collapse of the norm.

It is a sobering vision of wartime ethics that Thomas gives us, but also a healthily realistic one that—in its recognition of the leader's contrasting responsibilities to his or her fellow citizens and to an impartial system of ethics that grants equal rights to all, as fellow human beings—makes this book one of the most significant works in the field since Walzer's (1977, 1992) Just and Unjust Wars. He has made a real contribution to our understanding of this most terrible and central facet of international life.