The majority of armed conflicts in the world since World War II have been non-international. This includes the ongoing conflicts in Iraq, Afghanistan, and Syria, numerous past and present conflicts in various African countries, the various stages of the conflicts in the Caucasus region of Russia, civil wars like the case of Ceylon and those of the breakup of Yugoslavia, and conflicts involving on one side acts of terrorism under the auspices of groups like Al Qaeda and the IRA and on the other various forms of military response, as well as many other examples.¹ This is, for practical purposes, the new face of war, and it poses serious challenges to efforts, both legal and moral, to impose restraints on the conduct of armed conflict.

International law, on armed conflict as well as on everything else it treats, depends finally on agreements among states, and imposing the standards set in such agreements on armed conflicts that do not arise between or among states is hardly straightforward or in any way easy. The states in which such conflicts occur understandably claim precedence for their own domestic standards, including not only domestic laws but more permissive frames for emergency action by government forces against those challenging the government. Measures taken, or proposed to be taken, against non-state threats may controvert rights and liberties guaranteed to a state’s own citizens and may even, as an undesired but real effect, impinge on those rights and liberties. At the same time, the asymmetric nature of such conflicts mean that the particular forms of armed force employed will be different for each party to the conflict, the lines of division between combatants and noncombatants will be indistinct,² and lines of responsibility and accountability will intentionally be kept obscure on the side of insurgent forces. Existing international mechanisms aiming at limiting the harm done in armed conflict, as well as the specific limits themselves, do not transfer well to non-international conflicts; nor do the means of enforcement, which depend finally on the ability to gather information about the conduct of the parties to a conflict, function evenly or otherwise well when the focus is non-state armed groups whose very existence may hinge on closing off access by outsiders to information about their operational procedures. Finally, the most prominent example of an effort to craft positive international law so as to apply to non-international conflicts, 1977 Geneva Protocol II, has never attracted anything like the same level of state approval as the 1949 Geneva Conventions it intends to supplement. This does not provide an encouraging precedent. It has been suggested to me that customary law has by now closed various gaps left by Protocol II, and that may be so in certain respects, though I suggest the degree to which it has done so is far from self-evident, and there are importantly different conceptions of what constitutes customary law.

Approaching non-international armed conflicts from the standpoint of ethics has its own difficulties. Contemporary ethical reflection and discourse on armed conflict takes place largely through one or another form of just war thinking, but any review of recent discourse on just war shows widespread disagreement as to what the idea of just war is, what is the proper way of drawing out its meaning, and what its implications may finally be for specific issues in contemporary armed conflict.³ Much of this thinking, moreover, is rooted in debates about potential and actual uses of armed force by the United States against other states, and it has sometimes been argued that the just war idea has only to do with such state-against-state uses of force. The idea of just war was effectively lost as a basis for ethical reflection through much of the modern period and was only recovered in the context of debates over nuclear weapons and the Vietnam war, efforts that in fact reinvented the just war idea in different ways. Three major streams of recent just war thinking flow out of the work that defined that recovery and reinvention: Paul Ramsey’s books War and the Christian Conscience and The Just War, both from the 1960s,⁴ focused on the Christian ethical obligation of love of neighbor and reaching back to Augustine’s conception of divinely inspired love, caritas, for its foundation, whose influence is exemplified in recent work by Jean Bethke Elshtain, Oliver O’Donovan, and Nigel Biggar⁵; Michael Walzer’s 1977 book Just and Unjust Wars,⁶ whose conception of just war has influenced most recent philosophical thought on just war, though in different ways, as exemplified in the work of David Rodin,⁷ who follows Walzer in basing his conception of just war in human rights, and Jeff McMahan,⁸ who bases his version of just war in the requirements of individual ethics, developed by utilitarian moral reasoning; and finally, the United States Catholic bishops’ 1983 pastoral letter, The Challenge of Peace,⁹ which as a way of seeking compromise with Catholic pacifists defined their conception of just war as beginning with a general “presumption against war” and described an expanded list of criteria which, if all are satisfied, could overrule this general presumption in a particular case.¹⁰ This last conception of just war, which is functionally a form of modern-war pacifism, has influenced a number of Catholic thinkers, including later spokesmen for the bishops’ national conference, who have used it to oppose the use of force in even such cases as the action to reverse the Iraqi takeover of Kuwait in 1990–1991. More broadly, participants of various stripes in public policy debates have adopted the bishops’ list of just war criteria, which focuses heavily on their newly added criteria of last resort, reasonable hope of success, and overall proportionality. Besides these examples, a further new version of just war based on Kantian thinking has been advanced by philosopher Brian Orend.¹¹ Finally, my own conception of just war is based on what I regard as the classic statement of the just war idea, which originally coalesced in Western canonical and theological thought beginning in the twelfth century and remained stable as a cultural consensus until well into the modern period.¹² I describe this conception and its roots more fully in the following section as a way of defining the frame for my thinking about the matter of detention of enemies in non-international armed conflicts today. The differences among all these various “just war” positions are so substantial that recent just war thinkers are effectively at war with one another, rather than representing an ethical consensus. Much of recent just war thinking, moreover, has focused on limiting international wars and especially on restraining United States use of military force; when the subject has included non-international armed conflict, as is the case particularly for just war thinkers who have addressed terrorism and United States military efforts against it, the focus has remained on how the United States should behave.

The gist of what I have described above is that neither international law nor major forms of contemporary ethical discourse are well positioned to address the particular problems posed to efforts to restrain armed conflict of a non-international character. I would add that the loss of their common historical connection makes it difficult to pursue dialogue between international lawyers and ethicists. In the next section I move to explain further my own approach to contemporary ethical reasoning about armed conflict on the basis of the classic historical understanding of just war, which I will argue by its nature connects ethics and law and provides a useful basis for thinking about what is right and wrong in the context of non-international armed conflicts. In the final section I use the frame of thus established to directly address the matter of detention of enemies in non-international conflicts.

For an ethicist to write in a volume devoted to international humanitarian law will no doubt strike some readers as an anomaly: what do ethicists know about law, anyway? The differences in our uses of language noted above illustrate a conceptual divide: how we think about particular matters in armed conflict is not the same, and professionals on each side of the divide may fault those on the other for lack of precision or for simply getting the important issues wrong. For others, though, the recognition of such differences may perhaps serve as a reminder of the need for a dialogue that could be of use to both ethicists and lawyers, when such dialogue tends in fact to occur only sporadically and in limited contexts, without resulting in the creation of continuing personal interaction across the territorial lines of these two professional fields of discourse on the specific topic that brought the parties together for the moment. There are of course exceptions to this rather bleak view, some of the most notable being the continuing efforts exemplified by publications on particular topics that include chapters by both specialists in law and specialists in ethics. But at the end of the day most of the contributors to such interactions return to their own disciplinary frame, where by the nature of things it is difficult to incorporate whatever might have been learned from those working in a different frame, even if it might have seemed valuable to do so while the interaction was going on. I suggest an important reason the links between these two professional fields are in practice so hard to maintain traces to a loss of historical consciousness and knowledge in both. In setting out to explain the historically based conception of just war I work from, I reach back to the common roots of later legal and ethical thinking on the use of armed force on political authority, to a time when ethics and law were not the distinct fields they have since become.¹³

While the deep roots of the just war idea extend into classical Roman and Greek thought and political practice and into the biblical depictions of the wars of the ancient Israelites, and while the late classical Christian theologian Augustine drew on both these influences in a number of brief passages on just war found in various contexts in his writings, the creation of a coherent, systematic conception of just war came only in the Middle Ages. The original statement of such a conception appeared in the canonist Gratian’s 1148 compilation of canon law, the Decretum. This was debated, clarified, and more tightly focused by the contributions of two generations of his canonical successors, the Decretists and the Decretalists, over the next century. A succinct statement of their resulting position in a theological frame was provided by Thomas Aquinas in his Summa theologiae (II/II, Q. 40, “On War”) three-quarters of the way through the thirteenth century. The concept for which these writers used the phrase “just war,” bellum justum, focused on the moral conditions for resort to the use of armed force: who could authorize such resort (a temporal ruler with no temporal superior), a justifying cause (broadly, the vindication of justice when an injustice had been done; more specifically, as Aquinas puts it, quoting Augustine, the recovery of that which had been wrongly taken and the punishment of evildoers), and the governing intention (again understood through language taken from Augustine: negatively, the avoidance of wrong intentions such as those specified by Augustine in his treatise Contra Faustum XXII.75, and positively, the end of peace. Just war as thus conceived had directly to do with the exercise of government in the face of challenges to the fundamental purposes of political community. Though Aquinas used Augustine’s language to explain the necessary conditions for bellum justum, the three conditions he specified corresponded directly to the three goods of politics as identified in Roman thought—order, justice, and peace. The nature of good order (and thus the ruler’s responsibility) and of justice was defined here in terms of natural law, understood through the recovery of Roman legal thought that took place at the same time the just war conception was being pulled together and systematized. Bellum justum, thus defined, had to do with use of armed force by the supreme public authority for the public good, and was set off from two other kinds of use of such force by private persons for private reasons: duellum, dueling, the use of force between private parties to settle a dispute between them, and defensio, self-defense “on the spot” (incontinenti) against an immediate threat, understood to be a right given by natural law to everyone. Bellum justum sought to limit and even eliminate the former, since private parties could appeal to the highest ruler for adjudication of any dispute, and it supplemented self-defense “on the spot” by providing for repairing any injustice done and punishing those responsible for such injustice. In these functions bellum justum functioned juridically. The sovereign ruler, of course, had the responsibility of defensio against both internal and external threats to the interlocked order, justice, and peace of the political community, but this required no special notation in the definition of just cause for such a ruler to resort to armed force.

As thus described, bellum justum had to do with disturbances of public order, justice, and peace, whether these arose internally or externally. “Just war,” as we now translate this Latin term, did not refer specifically to conflicts between and among distinct political communities,¹⁴ as modern usage of the term “war” implies, but rather referred to the fundamental responsibility of the governing authority, given in the natural law, to protect and maintain a just and peaceful order in the community wherever a threat to it might arise. The classical conception of just war thus aimed at brigandage or crime by self-constituted armed bands as well as the unjust actions of subordinate warlords within the political community using the forces in their control for their own personal ends. Indeed, in the twelfth-century context, these were the main threats to the well-being of political communities. Among the three goods of politics order thus had the place of “first among equals,” since without right order there was no peace and no justice. Violence was endemic to medieval societies; descent of organized community life into anarchy was a persistent threat. But at the other extreme, a ruler with no superior might use the power at his command to become a tyrant. Thus the responsibility of the ruler was defined in terms of his responsibility for the good of the community as a whole and manifested specifically as the responsibility for vindicating justice. Neither anarchy nor tyranny did this: one was the absence of order, the other a wrongful order, and neither, in their neglect of justice, produced peace. Disputes might occur between sovereign rulers of different political communities which could ultimately be settled only by appeal to arms, but bellum justum