International relations scholars have long been working on how diplomacy can be understood by distinguishing diplomatic interactions in terms of multilateralism, bilateralism, and unilateralism. The so-called quantity-based approach focuses on the numbers of countries involved. Applying this framework, multilateralism needs more than three states in interactions; bilateralism needs two states; and unilateralism can be pursued by only a single state. However, there are more quality-based approaches to distinguish these interactions. Multilateralism requires states to follow international norms and pay more respect to international institutions; this is contrasted with unilateralism, where a single state can influence how international relations can be conducted. To understand multilateralism in foreign policy, it is crucial to understand how international society has developed institutions, norms, and regimes. By contrast, studies of unilateralism and bilateralism tend to focus on how a powerful state conducts its foreign policy by neglecting international institutions and legal constraints. This article introduces some recent evidence-based research on how multilateralism, bilateralism, and unilateralism are selected in a particular foreign policy area such as alliance formation, mediation, and international aid. The article covers how scholars frame research questions in each issue area and analyzes whether there are similarities or differences in research methods, data, and theoretical frameworks.
Multilateralism, bilateralism, and unilateralism are three interrelated but often complex concepts in international relations (IR). Some scholars separate these in simple terms of quantity: unilateralism is based on one state, bilateralism is based on two, and multilateralism has three or more (Keohane, 1990). By this definition, the United Nations (UN) is clearly a multilateral international institution—no one would think of the UN as a unilateral or bilateral institution. This simple numerical definition based on a “three-state minimum” criterion for multilateralism is seen by some as reasonable and practical (e.g., Corbetta & Dixon, 2004), but interestingly, this is a minority position in the field.
Instead, the majority of IR scholars employ a quality-based definition. This is the approach taken by Ruggie (1992, 1993) which suggests that multilateralism needs the following three features: indivisibility, generalized organizing principles, and diffuse reciprocity. Indivisibility requires multilateralism to be based around socially constructed public good (Ruggie, 1993, p. 11). Generalized organizing principles and diffuse reciprocity require multilateralism to be opposed to discrimination and preferential bilateralism. Thus, multilateralism denies “differentiation on a case-by-case basis according to power or individual preferences and demands for precise quid-pro-quo agreements—all of them are politics before 1945 ” (Weber, 1991, p. viii). As such, there needs to be cooperation on public goods and goods to meet the requirements of this quality-based definition of multilateralism. Additionally, the rules must be seen to apply to all countries: there must be no exceptions for powerful states.
Organizations formed at the end of the Second World War, such as the UN, the World Bank, the International Monetary Foundation (IMF) and the General Agreement on Tariffs and Trade (GATT) form the core of multilateralism, as they aim to include all of the world’s states as members. For instance, the Charter of the UN, its founding document, is based on several international rules that are applied equally to all nations, such as the principle of sovereign equality, prohibition of the use of force, and the principle of non-intervention.
Bilateralism, by contrast, is based on preferentialism and changes its goals and priorities on a case-by-case basis. 1 The collective security system under the UN Charter is clearly a product of multilateralism, but the collective defense system (known as collective self-defense) is based on preferentialism by the powerful states (such as the United States of America) and thus is a form of bilateralism. A typical example of bilateralism can be seen in the Asia-Pacific region where the United States formed a so-called hub-and-spoke type of alliances network (Hemmer & Katzenstein, 2002). In a similar vein, the North Atlantic Treaty Organization (NATO) could be seen as a product of bilateralism; however, some scholars believe that it is based on multilateralism among Western democracies in which shared norms and rules are applied to all on an equal basis (Weber, 1991). Since the Asian alliances with the United States are mostly bilateral treaties, and the terms of agreements vary considerably from country to country, the Asia-Pacific hub-and-spokes relationships can be seen as the product of bilateralism.
Finally, unilateralism is the term to describe a situation where the powerful state disrespects multilateral norms and adopts a self-centered foreign policy (Wedgwood, 2002). Power levels determine how unilateral a state can be. As such, unilateralism is the preferred course of action for the major powers and is more likely to be used by the hegemonic state (Wallace, 2002). A powerful state that can achieve its policy goals using its own resources without the need of international support can pursue a foreign policy that would not follow accepted international norms. However, such unilateral acts come with political costs (Thompson, 2009, p. 35) since unilateralism is often perceived as illegitimate, selfish conduct that damages the soft power of the unilateralist state. A good example of unilateralism can be seen in the actions of the then President-elect Donald Trump who before his inauguration in December 2016 declared the Trans-Pacific Strategic Economic Partnership Agreement (TPP) nullified, without seeking understanding from other participating countries. The United States was able to act in this unilateralist way because it was the largest economy in the TPP group, and its withdrawal would destroy the multilaterally concluded international free trade agreement.
In sum, multilateralism is at one end of a spectrum, based on norms and rules that sustain predictability in the international system and maintained (relatively) successfully by the strong leadership of the United States and its allied countries. At the other end of this spectrum, we find both bilateralism and unilateralism: bilateralism explores how international sets of standards can be modified by the agreement of two states (sometimes with pressure from a stronger state), and unilateralism describes a situation where the powerful state single-handedly (without the approval of its counterpart) takes certain measures that would not fit into existing international norms or rules.
Wedgwood (2002) makes one of the most important contributions to this field. Looking at both the quantity- and quality-based definitions, she builds an analytical framework to understand uni-, bi- and multilateralism. She argues that there are several meanings of multilateralism.
To explain these different understandings of multilateralism, she first looks at the difference between operation and authorization. This distinction is often used in both theoretical and empirical studies (Finnemore, 2003, Tago, 2005, Wolford, 2015). Multilateralism in operation can be referred to as “military multilateralism” when it concerns the use of force (Wolford, 2015, p. 23) and is conducted in a multilateral way (i.e., with the majority of states in international society). By contrast, a single country operation without help from others would be referred to as a unilateral use of force. The authorization aspect of multilateralism can be referred to as “diplomatic multilateralism” (Tago, 2005; Ikeda & Tago, 2014). This type of multilateralism is concerned with how a policy is approved by international society, or more specifically, a responsible international institution such as the United Nations Security Council (UNSC). Here we would also see examples of unilateralism if there is no approval from the UNSC or any other multilateral organization. Wedgwood goes on to argue that multilateralism can be understood from either a prohibitory or mandatory perspective. Depending on how international rules are interpreted by states, multilateralism norms can be about the prohibition of certain acts (such as mass killing) or the mandating of other acts (such as capturing pirates on the high seas). Again, unilateralism would be the corresponding term to these types of multilateralism. Ignoring either prohibitory or mandatory multilateralism would be considered unilateralism. Unilateralism against prohibitory rules would be described as exceptionalism, whereas unilateralism against mandatory rules does not have a corresponding “-ism”; instead, it may very well be ignored, due to the lack of capabilities or resources to do anything about it. In general, only major powers pursue unilateralism against prohibitory rules. For example, U.S. exceptionalism allows it to opt out of prohibitory rules of international relations such as the International Criminal Court.
In a similar vein, the processes of international actions and the subsequent decisions made provide us with an important analytical base. This enables us to think of a mixture of the three “-isms” (uni-, bi-, and multilateralism) in foreign policy processes. In the UN Security Council, some key decisions were made by the strong leadership of a powerful state (such as in the wars in Korea and the Persian Gulf); these can be regarded as unilateralism under multilateral cover (Wedgwood, 2002, p. 176). Also, during the Cold War, most of the important international deals were made by bilateralism between the United States and Soviet Union within the overall multilateral international order (examples include the Nuclear Non-Proliferation Treaty). Indeed, it could be possible in the near future that Sino–U.S. bilateralism may form the interregional, multilateral order of the Asia-Pacific region.
Miles Kahler takes this framework a step further, arguing that there has been a mixture of multilateralism, “minilateralism” and bilateralism since 1945 (Kahler, 1992, pp. 299–305). By way of an example, Kahler argues that the United States had attempted to generate a truly global, multilateral institutional network to solve public problems in the world. But due to confrontation with the Soviet Union, the United States had to drop these plans and form a more limited liberal international order by using minilateral cooperation with the allied states in Europe and Japan. 2 The minilateral great power collaboration of these countries was applied to the variety of collective action problems posed by multilateral governance such as free trade, the law of the sea, and so on.
As was shown in the previous section, the three “-isms” have been analyzed closely in relation to hegemony and international order. John Ikenberry (2000) argues that the hegemonic state (after “victory”) exercises unilateral leadership to fashion its favored form of international order. Yet this new order could be based on the norm of multilateralism (Ruggie, 1982; Stein, 1984). Taking advantage of its hegemonic rule during the 19th century , the United Kingdom pursued its policy of spreading the idea of free trade mainly by its unilateral control of the major trade routes. The idea of free trade was based on multilateralism, since it could be applied to all sovereign states.
Likewise, after the end of the Second World War, the United States took a unilateral lead and designed the postwar international order, which was based on the idea of multilateralism (i.e., indivisibility, generalized organizing principles, and diffuse reciprocity). The United States invited the United Nations to establish its headquarters in New York and regarded the institution as a core organization for international peace and security (it was so designed by introducing Article 2(4) [prohibition of the use of force], chapter 7 [allowing the use of force with UN Security Council authorization] and Article 51 [allowing the use of force under the right of individual and collective self-defense]). Furthermore, it created the International Monetary Fund to help with currency stability and the World Bank to finance the recovery of the global economy through investing money in infrastructure and reconstruction after the war. Fortunately, this unilateral leadership was warmly accepted by Western states, and these institutions gathered a large membership. However, its unilateral call for the creation of a free trade international organization, the “International Trade Organization” failed due to opposition from some countries and also from opposition by key actors within the United States. The United States had to give up and ended with a much weaker institution known as the GATT.
These examples show that unilateralist actions by hegemonic states are needed to introduce multilateralism in the postwar international order. 3 In principle, multilateral negotiations on multilateral norms without proper leadership would take more time (or could easily fail) since there would be more states involved in multilateral negotiations (i.e., it would be harder to find a solution that could be acceptable to all concerned parties), and they would not easily reach an agreeable outcome; leadership by a strong state is key to arriving at a form of international order which is potentially acceptable to all. Interestingly, in this mechanism, unilateralism helps multilateralism.
The American-made postwar international order driven by unilateralist leadership, however, exhibited both multilateral and bilateral characteristics (Ruggie, 1996). In Europe, the United States was consistent in its multilateralism by constructing and fortifying the NATO framework; by contrast, in Asia-Pacific, the United States tried to generate multiple, bilateral alliance ties (e.g., U.S.-Japan, U.S.-ROK, and U.S.-Philippines). This Asia-Pacific security regime was referred to as the “hub and spokes.” In a similar vein, the United States provided economic aid through a multilateral system in Europe. Alongside Canada, it created the Organization for European Economic Cooperation (OEEC) to deliver aid, which later became the Organization for Economic Co-operation and Development (OECD) in 1961 . In Asia, American aid was delivered on a more bilateral basis. For Latin American countries, the Organization of American States (OAS) was a symbol of multilateralism, and on some occasions the United States even used the system for military action (such as the 1965 Dominican Intervention), but on many other occasions, its relationship with Latin American countries was managed by bilateralism, based on factors such as whether the state would be a good U.S. ally, or levels of human rights protection (Cingranelli & Pasquarello, 1985).
Although American multilateralism has provided relatively stable international order and has led to economic prosperity for members of the Western bloc during the Cold War and even among the countries in the former Eastern bloc after the end of Cold War, the system now is facing at least two challenges: one internal and one external. The internal challenge is President Donald Trump, who came into power in January 2017 . He seems to prefer bilateral “deals” on trade and is reluctant to maintain a multilateral free trade framework. His unilateral “executive order” diplomacy clearly contradicts the United States’ past unilateral leadership in generating a multilateralist international order. It is hard to tell exactly where American foreign policy under President Trump is heading, but it will be a major challenge for the tradition of multilateralism, which was somehow respected even under conservative Republican presidencies such as those of Ronald Reagan and George W. Bush. 4
Multilateralism, as John Ikenberry and John Ruggie suggest, is the core of the current international order, designed by the United States after the Second World War. However, by the very nature of international relations, bilateralism and unilateralism are what states usually adopt as a tool of foreign policy, and thus multilateralism could be an exception.
We can understand this from some specific data. For instance, the default approach for American use of force is unilateralism (Tago, 2005). About 80% of its uses of force were carried out by its military without a partner state or authorization from an international organization. From 1948 to 1998 , U.S. presidents used military force 212 times, and in only 45 of these cases was the use of force embedded in a multilateral context. Moreover, 16% of the military alliances documented in the Alliance Treaty Obligations and Provisions (ATOP) data set between 1815 and 2003 were multilateral (Fordham & Poast, 2016). That is, 84% of the alliances were bilateral ones. International mediation efforts, which by definition sound like multilateral approaches, surprisingly saw limited cases of multilateralism. According to Böhmelt (2012), about 70% (219 out of 330) of disputes from 1945 to 2001 saw unilateral mediation. 7 In a similar vein, Milner (2006, p. 110) suggests that the median amount of multilateral aid committed relative to total aid is about 32%. The “norm” is bilateral aid-giving. Furthermore, Morgan, Bapat, and Kobayashi (2014) show that, out of 1,024 total cases of economic sanctions, 335 cases (33%) were multilateral. Again, unilateral sanctions form the majority of cases.
These data imply that unilateralism and bilateralism exist as a base choice for most policy areas. Uses of force are more often performed by unilateralism; alliances are formed in a bilateral fashion. Bilateral aid, unilateral mediation efforts, or unilateral economic sanctions are the majority policy approach in international relations. If this is the case, we need to answer why states select multilateralism on some (special) occasions.
First of all, some scholars may point out that multilateralism brings a better outcome; on sanctions, for instance, empirical research suggests that multilateral sanctions are more likely to be effective than unilateral sanctions (Bapat & Morgan, 2009; Morgan, Bapat, & Kobayashi, 2014). Based on their restrictive definition of successful outcomes, 51% of multilateral sanctions produced “success” as opposed to only 31% of unilateral sanctions efforts. For use of force, Graham, Gartzke, and Fariss (2015) show empirical evidence that coalition-based (thus quantity-based multilateralism) uses of force in militarized interstate disputes end with a better outcome (i.e., military victory). Quite why we see more instances of bilateral and unilateral approaches to foreign policy is therefore something of a puzzle. A better outcome would not always be assured and in some cases, unilateralism and bilateralism are the preferred choice of states.
For those who consider that unilateralism and bilateralism are better, it is important to note that they come with freedom of action and no transaction costs (Malone & Khong, 2003). Multilateralism imposes restrictions and requires states to devote more time and diplomatic effort to reach to an agreement. While UN approval would bring a higher legitimacy and thus garner wider support for the use of force, 8 a single state cannot decide what the coalition forces should and should not do. The cost of coordination among the coalition participating states should not be ignored (Weitsman, 2013).
In the field of military and national security, in addition to legitimacy, burden sharing would be an attractive feature of choosing multilateralism (Lake, 1999, 2009; Wolford, 2015). Burden sharing could be crucial when a state cannot mobilize its own resources but needs a large amount of capability to achieve a policy goal. For international aid, avoiding politicization and informational advantage could be the motives for multilateralism (Rodrik, 1996). Multilateral aid can remove the name of country giving aid; this could be convenient when a state does not wish its name to be revealed as a donor. As to the advantage in information, multilateral institutions could be in a better position to gather rich data on a recipient country and may know better as to where the aid should be allocated. Moreover, Milner (2006) argued that multilateral aid is necessary to justify the aid-giving policy to the general public who would be reluctant to support international aid—again, legitimacy would be a benefit of multilateralism.
In a nutshell, while facing with some costs of coordination, states in need of legitimacy, burden sharing, information advantage or avoiding being politicized would use a multilateral course of action in its foreign policy enthusiastically. 9
Finally, some scholars suggest the importance of domestic sources of multilateralism, bilateralism, and unilateralism (e.g., Kane, 2006). Tago (2005) specified that economic recession and divided government in U.S. politics tends to lead to multilateral military action since presidents need more allied support when Congress tightens the budget (under a recession) and is less likely to approve presidential initiative of military operation (under a divided government). Skidmore (2005, pp. 219–222) suggested that there are at least three types of anti-multilateralist groups in the United States—special interest groups, the military-industrial complex, and individuals motivated by “patriotism”—and that they play a significant role in shaping American unilateralism. In particular, special interest groups may lobby against international and multilateral initiatives that they believe harmful to their business. For instance, particular energy industries (such as oil and gas companies) opposed the Kyoto and Paris scheme on climate change. The National Rifle Association objected to a small arms control treaty and thus the U.S. government could not take a lead in a possibly critical international regime that could effectively counter a risk of terrorism and civil wars. Skidmore (2005, p. 221) hypothetically suggests that relatively lower level of interdependence for the United States allows it to follow the anti-multilateralist’s call for unilateral policies than its European countries and Japan, which are highly dependent on each other and cannot survive without multilateral schemes.
In the end, this essay concludes with a short introduction on game theoretical analysis of the three “isms.” In the history of the development of these concepts, scholars have used game theory frameworks, and these should not be ignored in an article such as this. This is particularly true for multilateralism and multilateral institutions, which are different but closely interrelated concepts in explaining international cooperation (e.g., Martin, 1992a; Fang, 2010; Okada, 2017).
When states engage in rule setting for international industrial standards, they will face a coordination problem, and this will require the help of multilateralism. Figure 1 shows a typical coordination game with divergent interests (Martin, 1992b, p. 101). States A and B can select either X or Y option (both X and Y are concerning some international standard). Assume that State A is taking X standard and State B is taking Y. For both states, mutual standards coordination would bring a larger (combined) market and thus would be beneficial. Unilateral standard setting in each country and thus a noncoordinated state of the world ([Y, X] and [X, Y]) is inferior to a coordinated state of the world ([X, X] and [Y, Y]). In this game, there is no dominant strategy for each; the best response is dependent on how other player behaves.
Figure 1. A Coordination Game with Divergent Interests
In this framework, the coordinated states of the world, [X, X] and [Y, Y] are the Nash Equilibrium. Therefore, as Martin suggests that “coordination games do not require institutions with strong mechanisms for surveillance and enforcement” (Martin, 1992b, p. 101), multilateral institutions will not be necessary once it is determined which standard should be an agreed one.
However, to determine which coordinated reality should be achieved, States A and B would need a multilateral forum to negotiate and multilateralism to reach an agreement. In the above example, State A would push standard X and State B would propose standard Y, respectively. Martin (1992b, p. 101) suggested that general multilateral principles (institutions of multilateralism, such as, for example, indivisibility and diffuse reciprocity) could play a central role in enabling states to effectively reach a particular outcome (for instance, a series of bilateral bargaining negotiations would be highly inefficient for finding what would be a widely agreeable international standard; discrimination also does not make sense in this type of problem setting). The decision-making procedure for those negotiations would require multilateral legitimacy, and such a procedure may be a source of disagreement. This is because the decision-making rules could critically affect the outcome by giving a clear advantage to a particular party to the negotiations.
By contrast, in a setting as known as the Prisoners’ Dilemma or collaboration game (see Figure 2), only multilateral organizations (not multilateralism) would find a further role in achieving international cooperation. Think of option X as disarmament and Y as armament (of, say, nuclear weapons). Situations where the arming state faces a disarming counterpart (thus [X, Y] and [Y, X]) are the best for the arming state and the worst for the disarming country. While mutual disarmament is ideal (for preventing nuclear war among states) and less costly for both, it is an unstable state of the world since the players have incentives to move to arming (i.e., mutual disarmament agreement would face a cheating incentive). In other words, in this game, players have a dominant strategy of taking option Y and ending up with mutual armament, which is the Nash Equilibrium.
Figure 2. A Collaboration Game
In this type of problem, according to Martin (1992b, p. 95), multilateral organizations “can play a role in facilitating cooperation,” but multilateralism as a collection of norms does “not meet the demands of collaboration games, leading us to expect divergence between the institution of multilateralism and multilateral organizations.”
While both of the collaboration and coordination games embody a symmetry of players’ preference order, in establishing multilateral institutions states may hold quite different, asymmetric interests over the outcome. 10 Assume that State A holds significantly more power and wealth than the others; in Martin’s (1992b, p. 103) words “It frequently formed a privileged group of one” and is likely to unilaterally take the lead on a particular policy such as the control of sensitive technologies (i.e., prohibiting its technology transfer to a competing, rival state and asking State B to follow a similar course of action). In this situation, smaller states (i.e., State B) would have a strong incentive to cheat and free ride (i.e., exporting items with sensitive technologies to the rival state and gain benefits). A typical suasion game, such as that presented in Figure 3, shows how two players can have asymmetric interests. State A has a dominant strategy of choosing X (i.e., prohibition of technology transfer to a rival state), while State B can gain the highest interest if it selects Y when State A chooses X.
Figure 3. A Suasion Game
According to Martin (1992b, p. 105), there is little reason to believe that multilateralism as a collection of norms would play a significant role in guiding smaller states’ behavior to select option X. Nondiscrimination norms would not function since the hegemonic state cannot effectively threaten retaliation against the smaller states’ defection (the smaller states know that the stronger state will select X no matter what).
Finally, a different asymmetric-interests setting can also exist. Figure 4 is a typical case of an assurance game where states have higher interests in mutual cooperation (here we assume that X is a choice of cooperation and thus [X, X] is mutual cooperation). Rational states with complete information would cooperate with each other. Even though mutual defection (i.e., [Y, Y]) would be Nash Equilibrium, [X, X] is far better for both players (Pareto-superior), and thus it would become a focal point. In this setting, multilateralism may be critically important for making players be transparent with each other (thus allowing states to achieve complete information) without discrimination. 11
Figure 4. An Assurance Game
Multilateralism, whether conceived as a quantity-based definition (foreign policy for more than three states with strategic interactions) or a quality-based definition (foreign policy based respect for international order with indivisibility, generalized organizing principles, and diffuse reciprocity norms), is contrasted with bilateralism and unilateralism. Bilateral deals and a dyadic understanding of international relations, or unilateral engagement and exceptionalism, are different from what a multilateralist foreign policy approach assumes. We must note that since Second World War, the international order has been designed by the hegemonic power (the United States) based on its multilateralist norms even though it could be now facing serious challenges from both within and from outside this order as well. Since multilateralism would require a relatively high transaction cost and ties the hands of nations (through the loss of freedom of action), bilateralism and unilateralism would be the base choice for foreign policy for most states and in most issues. However, multilateralism would be selected when the benefits of legitimacy, information advantage, and burden sharing are desired. As it has been always so in international relations, a mixture of multilateralism, bilateralism, and unilateralism is what we will observe in international relations. This should be especially true when a hegemonic power is on the wane and a nascent multipolar international system has been emerging—and where no state can be so powerful as to act in a solely unilateral way and force the other states to engage with it via bilateral negotiations and bilateral coordination.
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