The increasingly widespread and energetic engagement with the idea of just war over the last fifty years of thinking on morality and armed conflict--especially in English-speaking countries--presents a striking contrast to the previous several centuries, going back to the early 1600s, in which thinkers addressing moral issues related to war did so without reference to the just war idea.
From the late twelfth century to the early seventeenth century a well-defined tradition on just war enjoyed broad cultural acceptance in the West. This framed the resort to force in terms of the responsibilities of sovereign political rule and the political ends of order, justice, and peace, and established limits on conduct in the use of justified force. This tradition had been shaped by philosophical, theological, and political thinking on natural law, by military thought and practice, by legal traditions reaching back into Roman law, and by accumulated experience in the government of political communities. In the cultural context of the Middle Ages, all these overlapped and interpenetrated one another to an important degree. (1)
But under the conditions of the Modern Age this cultural consensus broke down, and the various fields of influence that had shaped the earlier tradition on just war became increasingly distinct from one another and so tended to lose contact with one another. (2) In some arenas creative efforts to engage the idea of just war disappeared altogether: for example, the Spanish Jesuit Francisco Suarez (1548-1617) and the English Puritan William Ames (1576-1633) were the last important theological writers to do so until the twentieth century. In other arenas the ideas defined and set in relationship with one another within the historical just war tradition were redefined and rearranged into new frames of thinking, in which these ideas remained, but their links to earlier just war tradition were downplayed and gradually forgotten.
This was the case with modern thinking on international law, which is heavily indebted to Grotius's reframing of the inherited tradition of just war into his conception of the law of nations in his influential De Jure Belli ac Pacis (On the Laws of War and Peace), first published in 1625. (3) In regard to this latter line of development, I have argued that in this way the just war tradition was effectively transformed into a tradition of law, and basic concepts from the earlier tradition on just war were thus maintained as legal ideas right up to the present. (4) A forceful presentation and documentation of this historical relationship is provided by Classics of International Law, a Carnegie Institution series mostly published between the two world wars. (5) But most contemporary international lawyers ignore this historical connection between the law and the idea of just war, treating the law simply as a product of positive agreements among states.
In any case, by the beginning of the early seventeenth century the connection to the idea of just war as defined in the historical tradition had been transformed and effectively lost as a basis for creative, systematic moral reflection on war. While the Carnegie Institution series did valuable service in making available the writings of a broad variety of thinkers who worked with the just war tradition that they had inherited and who laid the groundwork for the transformation associated with Grotius, it did not lead to new systematic thinking around the idea of just war. Indeed, while its last volumes were still flesh from the press, Reinhold Niebuhr, in his important theological work The Nature and Destiny of Man (1941), derided and rejected what he called "the Catholic theory of a 'just war'" (despite the broad use of the inherited just war tradition by Protestant thinkers in the Reformation era) in the process of an extended criticism of the Catholic conception of natural law (which he identified with the theology of Thomas Aquinas). Niebuhr here showed no knowledge of the broader historical tradition of just war or the rich tradition of moral and political theoretical reflection associated with it, but to recognize this is part of my point about the general loss of consciousness of this tradition: in this he exemplified his generation and those before him. For his conception of just war, Niebuhr provided only a brief quote from Suarez's Tractatus de Legibus--including the following, which he made the focus of his criticism: "First, it must be waged by a legitimate power. Secondly, its cause must be just and right. Thirdly, just methods must be used." Niebuhr then went on to dismiss the concept as assuming "obvious distinctions" between "justice" and "injustice" and between "defense" and "aggression," despite the fact that judgments on these matters are "influenced by passions and interests." (6) Niebuhr did not know Suarez's longer, focused, and detailed treatment of just war in the work devoted fully to it, De Bello, which provides an extended discussion that presents the matter of justice in war not in terms of absolute certainty (as Niebuhr wrongly argues), but in careful and nuanced language about making judgments among relative claims. (7) The broader just war tradition is full of such discussion. But what Niebuhr read from the short passage of Suarez allowed him to make the point that he desired (which had been forged in his rejection of pacifism in the 1930s): that the use of armed force may sometimes be necessary, but that it is never without injustice and is always tragic. Thus, just war thinking, as Niebuhr depicted it, is accordingly irrelevant, introduced simply for the purpose of being rejected. (8)
The Two Main Avenues of Criticism of Just War Thinking: Political Realism and Pacifism
Up through World War II and the beginnings of the nuclear age, Niebuhr's position represented one of the major options for mainstream American Protestantism; the other was a form of pacifism based on the ideal of abolishing war through the creation of a world order by international law. In broad terms, these two options have remained as the twin avenues of criticism of the idea of just war: realism and pacifism.
While Niebuhr is generally recognized as being one of the architects of political realism (the other being Hans Morgenthau), present-day political realism has evolved into a rather more simplistic position than Niebuhr's, having become identified with the rejection of any place for moral values in the sphere of practical politics and the insistence that political decision-making should instead be based on interests alone. This is a conception that traces to neither Niebuhr nor Morgenthau but to Robert Osgood's Ideals and Self-Interest in America's Foreign Relations (1953). (9) From this latter perspective, what is wrong with just war reasoning is that it injects value considerations into policy and practical decisions about the use of military force by states and nonstate groups, and attempts to set limits on the use of such force even at the expense of national interests. This conception of realism is problematic on its own terms, as the interests of a state or nonstate group inherently reflect that entity's defining values; the interests would be worth nothing if they did not. More precisely, then, the realist criticism of just war thinking should be understood as proceeding from a clash of values between those expressed in the realist conception of national interest and those expressed in the just war idea. Understood this way, the criticism deserves attention, though it is hardly devastating to the just war idea.
The nature and effects of pacifist criticism of just war thinking are more complex and harder to evaluate. To think about pacifism more precisely, there are two main kinds that can be identified: one rooted in the moral rejection of all use of violence and another rooted in an abhorrence of the destructiveness of war, an association of war with the system of rival states, and the ideal of abolishing war by bringing into being a universal government replacing the state system. (10) Each has taken a variety of historical forms, and in some circumstances they have made common cause. Pacifist criticism of just war thinking has varied accordingly. Historically, pacifism of the first sort has produced sectarian movements advocating withdrawal from society, but this is not how contemporary pacifists have operated. Rather--as we can see, for example, from the activities of the Peace Churches--they have sought to establish mechanisms for resolution of conflicts and reconciliation, both of which can be viewed as challenges to the just war-based idea that at least some conflicts require the use of force to resolve and correct injustices. A second example is that of the Pax Christi movement in American Catholicism, to whose influence the signature idea in the 1983 U.S. Catholic Bishops' Pastoral Letter on War and Peace, The Challenge of Peace, can be traced: the notion that Catholic just war thinking always begins with a "presumption against war" as something inherently sinful and to be avoided. (11) This is a pacifist idea; just war tradition in fact treated the use of armed force under the conditions of just war as serving a moral good by combating threats to justice, good order, and peace. As for world-order pacifism, historically this was manifested in support for the League of Nations and the United Nations, and in general it shows up in opposition to any use of force that might serve national interests. Another example is provided by David Rodin's argument (discussed below), whereby the idea of just war can be realized only in the case of a universal government that uses force to police injustice.
In my judgment, pacifist criticism has been more effective than that of political realism, in that it has pressed the idea of just war to be more in line with pacifist ideals, and has thus undermined and displaced...