In any society, regulating the use of force among members is a foundational and defining task. How force is used among members of a society, by whom, and to what purpose reveal a great deal about the nature of authority in the group and the ends that its members value. Force need not be eliminated as a prerequisite for social life—quite the contrary. Many, probably most, societies throughout history that we have come to respect as exemplars of civilization engaged in exceptionally violent practices. Rome comes to mind as one such instance. Many societies, our own included, celebrate certain types of violence, rewarding martial success or skill at arms. Violence or the potential for violence is a fact of human existence. Societies, to cohere and function, must come to some understanding of the role force can or should play in the society members’ collective life. That role may be large or small, but it is not random. Force is channeled and disciplined by the notions that members of a society share about when force is legitimate and what kinds of goals it can achieve.

Like any society, international society has shared notions that shape the use of force. One is that large-scale force is the prerogative of states. We live in a world of states that, in turn, are defined by their supposed monopoly on the use of force in their territory. Violence by non-state actors is branded as illegitimate, and its perpetrators are hunted down by states, often acting collectively in the name of “the international community.”1 The use of force between states is also shaped by the notions people have about rights and duties of states toward one another. Violations of those shared understandings constitute causes for military action that states collectively understand and recognize. Similarly there are rules about how military force may be used by one state against another—which weapons may be used, who may use violence and who may be its target, how intermediaries are to be treated and communication maintained.2

In this book I examine one particular use of force, military intervention, as a window onto the changing character of international society—the purpose to which its members will use force, the ends they value. In a society that has no central government or law enforcement, those with the means to do so enforce understandings of right and permissible conduct. In international society, intervention and ultimately war are the most visible and perhaps most consequential ways of enforcing standards of conduct, but they are also the most costly. Unlike some war situations, intervenors usually have a choice about whether to use force, and those choices are revealing. States debate long and hard, both within themselves and among themselves, about whether to intervene, who should intervene, and what social values, exactly, are being secured by uses of force. At a behavioral level, it is these enforcement actions that establish the basic rules of the system about what action is permitted and where the boundaries of sovereign control lie. At the cognitive and normative levels, it is the debates surrounding interventions that establish the authority and legitimacy of those rules. Rules backed only by force, without any legitimacy or normative authority, are difficult to sustain and tend not to last long.

Patterns of military intervention have changed over the history of the states system. States used to intervene militarily in other states for reasons and in ways that they no longer do. States now intervene for reasons and in ways that were unimaginable one hundred or two hundred years ago. This book investigates these changes and the processes that have brought them about. Dominant arguments in security studies would expect these changes to be the result of material factors such as alterations in the balance of power or in the offense-defense balance. However, I argue that many of these changed patterns of military intervention are not the result of new weapons technologies or altered power capabilities in the system, nor have the number or scale of interventions changed markedly. Strong states continue to intervene in weaker states on a massive scale when it suits them. What has changed is when it will suit them—not the fact of intervention but its form and meaning. What have changed are state understandings about the purposes to which they can and should use force.

That understandings about force would vary among states and across time is hardly surprising. States, after all, are a varied lot. We have good theoretical reasons to expect differently constituted and differently situated states to use military force differently. Democratic states might intervene in a different pattern than militaristic authoritarian ones; industrialized states might intervene differently than developing states; states more integrated into the global economy might have interests prompting different patterns of intervention than more autarkic or insulated states. What is interesting about the patterns of intervention investigated here is that the changes in these patterns are global. Certain kinds of intervention states used to engage in have simply disappeared. Others have been created or changed in a systemwide fashion. In all cases, states as a group have rejected intervention for some purpose or have altered their understandings about how or why intervention is done, with the result that the behavior of states has changed across the system. My goal in this book is, first, to document that these changes have occurred and, second, to try to understand how and why they happened.

I examine three cases of systemic change in intervention behavior. In one I investigate intervention to collect debts. States used to be able to intervene legitimately to collect debts owed to their nationals by other states. The practice stopped in the early twentieth century. Why? I examine an array of possible answers having to do with rising U.S. power and changed economic structures but find little positive evidence for these explanations. I argue that a variation in the professional composition of decision-making bodies was central to this change. Specifically the rise of international law as a profession, and the increased presence of lawyers at international conferences and treaty negotiations, meant that legal solutions to conflict, such as arbitration, came to be perceived by states as both morally superior and more useful than military solutions, such as intervention. In another case I examine humanitarian military intervention and show that, although states have been intervening for this purpose for at least two centuries, whom they protect and how they intervene to do so have both changed. States now entertain claims from non-white, non-Christian people who previously would not have registered on their consciousness, and, when they intervene, they will do so now only multilaterally with authorization from an international organization. Since multilateralism is often not burden sharing in a meaningful material sense, and since these international organizations often have poor track records as military commands, the move to multilateralism requires some explanation. Finally, I examine the very common claim states make that they are intervening because the target state presents a threat to international peace and order. As with humanitarian intervention, states have been intervening for this reason for centuries, but the way they understand order has varied and the ways they intervene to promote or protect it have consequently changed as well. If one thinks that one lives in a balance of power, one intervenes differently than if one lives either in a concert, a spheres-of-influence system, or the current system. Further, I show that the type of order states construct is not consistently correlated with the material distribution of power. States can (and have) constructed a balance of power, for example, in the midst of material hegemony or bipolarity.

One striking feature of all these cases is their apparent “obviousness.” Of course we no longer intervene militarily to collect debts. There are obviously much easier and more effective means of accomplishing this end. Of course people who are neither white nor Christian are still human, and we should intervene to protect them if we can. To think and do otherwise would be racist and barbaric. Certainly we should have partners in any intervention and bring the international community on board through the United Nations or some other organization. This obviously reduces the military burden on us and reduces the political costs of intervening, making such action easier to “sell” at home and abroad.

There is an overwhelming tendency in analyses of intervention (and of politics generally) to treat motivations or interests as obvious and to take for granted the context that gives rise to them. Very often this is not a conscious choice analysts make. Most of us are products, and captives, of our own normative context, and, like the decision makers we analyze, we take a whole range of ideas, beliefs, and contexts for granted. Taking a broad historical perspective can be useful in this regard. Having done so here has prompted me to ask questions about matters that now seem obvious to us and to show that what appears obvious or necessary now was not always seen that way. Alternative views of the world and of the legitimacy or efficacy of force existed in each of the cases I examine. In all three situations, what is now “obvious” was, in earlier periods, vigorously contested or rejected for well-articulated and logical reasons. The goal of the case studies is to show how ideas about what states valued or what goals could be secured by force or both have changed, and not just in one state but in many.

This book makes several arguments aimed at different audiences. For traditional security scholars in international relations, my goal is to prompt new thinking about the very old problem of military intervention. Most writings about military intervention are loosely informed by realpolitik notions that strong states will intervene in weak ones when it serves their geostrategic and economic interests. The cases investigated here were chosen, in part, because they are not easily explained by this formulation. States do, at times, use force for other reasons, as the humanitarian intervention cases show. The more common problem with the traditional formulation is that interests are simply indeterminate. In almost any case of intervention, one could impute a very reasonable set of interests that would explain intervention and another equally plausible set that would explain nonintervention. In fact, in most cases these opposing conceptions of national interests actually were articulated and strongly pushed on decision makers by groups on different sides of the debate over whether to intervene. What is interesting, then, is not the claim that intervention serves interests; of greater note are the contentions about what state interests are and which interests intervention serves. By examining broad patterns of intervention behavior across the system and the kinds of debates states have had about intervention, one can begin to understand both the coordinated shifts in perceptions of interests among states and how it is that states understand the utility of intervention as a tool of policy.

For constructivists and legal scholars, the book goes on to examine how, exactly, changes in these interests and understandings have been accomplished. Over time, states construct rules among themselves about when intervention is legitimate or necessary. These rules are not divorced from power or interests. To the contrary, rules about intervention are strongly if not entirely shaped by the actions of powerful states that actually have the capacity to intervene. The issue explored here is how one set of rules perceived by the powerful to be “in their interest” is replaced by a different set of equally self-interested rules. Historical context and contingency play a role here, but so does purposive agency. In all three cases, I examine processes of what I have elsewhere termed “strategic social construction,” whereby actors consciously set out to change the perceptions and values of others.3 Elihu Root, Luis Drago, William Gladstone, Robert Castlereagh, and Clemens Metternich all consciously set out to change the rules about intervention and the way their contemporaries understood legitimate uses of force. Sometimes they succeeded, at other times they failed, but the tools and techniques they used to accomplish this task of persuasion are foundational to any understanding of the changing normative fabric of world politics. Exploring these techniques of persuasion and how or why they work leads me to connections with both psychology and diplomacy in ways that I hope will be of interest to international relations scholars generally.

Finally, for those interested in normative theory and ethics, the book examines some of the contradictions in intervention norms and their implications for policy. Because military intervention, by its nature, involves violation of a foundational principle of international law (sovereignty) and of a central ethical component of international community (self-determination), it almost always prompts extended normative discussions, both within and among states, about what is right and good in international life. As the cases here reveal, most interventions are embedded in some kind of normative conflict that creates difficult choices for participants. The sanctity of contract must be weighed against state sovereignty (chapter 2). Normative imperatives for humanitarian action to protect lives of innocents must be weighed against values we hold for self-determination and duty to protect one’s own citizens in uniform (chapter 3). Pursuit of self-determination, which we all profess to value so much, may impinge on the peace and security of others in the international community when force and revolution are the chosen ways to achieve it (chapter 4). The normative conflicts involved in each intervention are, of course, different, but the pattern of choices we make about those conflicts is not random. Over time, some normative claims become less powerful or have disappeared entirely. Glory acquired by success at arms is no longer a prominent goal of powerful states nor a justification for military intervention that is accepted by other states or mass publics. Other claims appear to be increasingly powerful, notably claims about human rights, which now challenge assertions about sovereignty and self-determination that were the trump cards of international normative discourse thirty years ago. These shifts by no means reduce normative conflict or intervention, but they do relocate conflict in ways that alter the purpose and character of military force over time.

This chapter begins with a brief discussion of intervention—what it is and why it is interesting theoretically. This is not a pro forma review, since, in many ways, the concept’s theoretical importance comes precisely from ambiguities about its definition. Intervention lies at the boundary of peace and war. It also defines the outer limits of sovereign control. It is this liminal character of the concept that makes it a useful vantage point from which to inquire about the role and purpose of force in international society, and the next section elaborates this point. The second section presents the agenda for the book’s empirical investigation. There are a variety of well-established and fairly obvious explanations for why intervention patterns change that I test in each chapter. The most prominent involve changes both in the distribution of material power and in military technology that make application of force possible where it was not possible previously. There are fewer available explanations for how patterns of intervention behavior might change. Explanations that locate causes (answers to the “why question”) in changing technology or distributions of material power rarely provide detailed explanations of how, exactly, decision makers change their notions or learn about these new material realities in ways that influence intervention. Similarly explanations that locate causes in changing rules, law, or norms about intervention rarely specify detailed mechanisms whereby decision makers become persuaded by new claims or follow new rules in considering intervention. In each case I cull what I can from previous research to develop expectations about where these mechanisms might be found and rely on induction from the cases to help elaborate several processes later in the book. The third section presents a brief overview of these findings and some of the themes that run through the cases. I became interested in this problem precisely because the discipline did not have good hypotheses about the changing purpose of force that I could test. Thus a major part of this project is the generation of new hypotheses and a sketching of the changing “normative landscape” on which new rules of intervention are negotiated. I find three major trends running through all three cases, and argue that these constitute basic features of the dyna...