Key Theories in International Relations

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Key Theories in International Relations

The following theories are the key theories in International Relations.


There are a wide range of realist theories. The common threads that bind them together are the beliefs that: (1) states act according to their own interests, (2) states are the primary actors in the international system, and (3) the international system is anarchic. Thucydides, Machiavelli, and Hobbes have all been referred to as “the first realist.” However, Reinhold Niebuhr was one of the first to consciously discuss international relations theory in realist terms. In Niebuhr 2013 he draws on political theorists and philosophers to show that while a person can act morally in the personal sphere, it is impossible for a person to behave morally in the political sphere. Carr (see Carr 2016) and Morgenthau (see Morgenthau 1993) follow in Niebuhr’s tradition and focus on the nature of man as the source of conflict. Where the utopians argued that perfecting man could end war, Carr and Morgenthau’s brand of classical realism seeks to find a balance between utopia and reality. Morgenthau takes a much more comprehensive approach than Carr. He attempts to produce a complete IR theory, while Carr’s primary aim is to dismantle utopian thought and argue for a balanced approach to policy. Carl Schmitt and Max Weber influenced Morgenthau’s thinking, and this relationship is discussed in many sources whose specificity keeps them from this bibliography. Aron (see Aron 2003) developed classical realism into a tool for foreign policy prescriptions. Structural realism (or neorealism) was developed by Kenneth Waltz as an attempt to bring science back into IR theory. It is divided into two major strains, “offensive realism,” developed in Mearsheimer 2014, and “defensive realism,” developed in Waltz 2010 and Waltz 2001. They share a common belief that it is not man’s innate lust for power that drives international conflict but rather the anarchic structure of the international system. For defensive realists it is possible for a state to have too much power, which makes the state less secure by provoking a balance of power. Thus, states should pursue security, and power may or may not be the means to that end. Mearsheimer argues that because a state can never divine the optimum amount of security to deter aggression without provoking balancing, it must always attempt to maximize power and not security. Thus, power is both the ends and the means. Neoclassical realism argues that policy must be filtered through the structure of the domestic government (Waltz’s “second image”—government) and the perceptions of the relevant policymakers (Waltz’s “first image”—people).


Liberal international relations theory is related to, but distinct from, the utopianism of the interwar period. The utopians believed that war could be eliminated either by perfecting man or by perfecting government. Angell 2009 is perhaps the most important and frequently cited explicitly utopian work. Angell argues that since war is, arguably, a money-losing proposition, people can end wars by teaching policymakers about their costs. Contemporary liberal IR theory may be related to utopianism, but its roots extend at least as far back as Immanuel Kant’s “Perpetual Peace,” written in 1795 (see Kant 2003, listed under Political Theory and IR Theory). In that essay, Kant provided three “definitive conditions” for perpetual peace, each of which became a dominant strain of post–World War II liberal IR theory. Institutional liberalism emphasizes the importance of international institutions in maintaining peace (Kant’s “federation of free states”). Keohane 1998 is the best short overview of this theory. Keohane argues that institutions work because they reduce transaction costs, increase transparency, and decrease uncertainty about other states’ intentions. Ikenberry 1998–1999 explains why institutions persist in what might be considered a realist world, and Ikenberry 2018 explains why the liberal world order will persist despite the rise of authoritarianism. Keohane and Nye 2011 argues that “complex interdependence” prevents states from going to war with each other. Institutions are also an important part of “collective security” (arguably a theory of its own): the idea that all states within a collective security arrangement will join forces to stop an aggressor (even one within the arrangement itself). Claude 1964 uses the history of the United Nations to provide a detailed discussion of collective security. Commercial liberalism emphasizes the importance of economic interdependence and free trade (Kant’s “universal hospitality”) in maintaining peace. Adam Smith is generally considered the father of this theory, though it is only a small part of his voluminous Wealth of Nations (Smith 2003). Democratic peace theory argues that democracies rarely, if ever, go to war with each other, and therefore an executive accountable to the people or the parliament is important to maintain peace (Kant’s call for states to have “republican constitutions”). The authors of Russett and Oneal 2001 use a large-n quantitative study to show that democracy is more important than institutions or economic interdependence in predicting the possibility of war. Doyle 1983 brought Kant back to the forefront of international relations and has been cited by well over one thousand subsequent sources. Howard 2008 provides a sweeping but concise overview of liberal foreign policy.


Constructivist theory emerged in the mid-1990s as a serious challenge to the dominant realist and liberal theoretical paradigms. Onuf 2013 coins the term and defines the paradigm, while Wendt 1992 (a direct challenge to neorealism) and Katzenstein 1996 have made it a staple of international relations syllabi around the world. This section focuses on what is sometimes referred to as “conventional constructivism,” or even “Wendtian constructivism,” in contrast to “critical constructivism,” which in this bibliography is treated as part of Critical IR Theory. Constructivist theory differs from realism and liberalism in its de-emphasis of objective measurements of power. The belief in the social construction of reality leads constructivist theory to place a greater role on norm development, identity, and ideational power than other theoretical paradigms. Texts that were written before the idea of constructivist IR theory was conceived could now be considered precursors to constructivist IR theory. Anderson 2016 is not the first, but it is influential among the early works by constructivist thinkers for its claim that national identity is socially constructed. Berger and Luckmann 1991 is a work of sociology important for constructivism because of its argument that objects and ideas are given meaning through social interaction. Checkel 1998 reviews some major constructivist books and provides a clear and readable, if not easy, overview of conventional constructivism. Hopf 1998 provides a clear example of the differences between conventional and critical constructivism. The search for an explanation about why states and the international system develop and adhere to norms is a crucial part of conventional constructivist theory. Katzenstein 1996 is perhaps the most widely taught and widely read work on the subject. Alexander Wendt is without question the most widely taught constructivist international relations theorist. Wendt 1987 shows that sociological methods, later popularized in IR by Wendt himself, could be applied to show that the system and its constituents are mutually constituted. Wendt 1992 takes apart Waltz’s argument that anarchy is a zero-sum game for states, by showing that anarchy has its own rules and that there can be different types of anarchy. Wendt 1999 is the first major attempt to mount a cohesive “social theory of international politics.” The book is a direct assault on Waltz and has had a profound influence in the field.

The “English School”

The English School, so named because its earliest proponents were colleagues at the London School of Economics, is treated as a separate branch of international relations (IR) theory because a strong case can be made that it belongs in any one of the three major branches listed above. At the undergraduate level, it is taught much more widely in the United Kingdom than anywhere else. The major innovations of the English School to IR theory were the addition of normative elements and the concept of “international society.” The term was coined in Jones 1981, and Jones claims that the major thinkers in the field had already begun to repeat themselves; he feared that there wasn’t enough “there” there to sustain a new and distinct theory. Though the term did not yet exist, Bull 2012 (first published in 1977) and Wight 2002 (first published in 1946) are perhaps the foundational texts of the English School. Bull argues that the anarchy present in international relations forms a society with its own rules and norms of behavior. Wight adds normative elements to IR theory. These normative elements may not seem to go far today, but at the time the idea was quite controversial. Hall 2006 presents a look at Wight the thinker and Wight the man, and it is useful for any in-depth look at the origins of the English School. Little 2000 provides a relatively brief overview of the English School and carves out a separate theoretical niche for the theory, distinct from the realism/liberalism/constructivism divide. He argues that the theory crosses each of them and blends many methodological and theoretical approaches. Dunne 1998 provides a longer overview of the English School. Reus-Smit 2002 compares the English School to constructivism and shows that they are distinct theories that have a lot to offer each other. Buzan 1993 compares and contrasts structural realism and regime theory (not explicitly included in this article) with the English School and imagines that the English School can be a bridge between realist and liberal theories.


The study of Marxism in the international relations (IR) theory classroom has been on a steady decline since the end of the Cold War. Any student of Marxism is wise to begin with Marx and Engels 1978, which is used in many disciplines and contains key Marxist texts, of which The Communist Manifesto is the most famous. Hobson 1965 (first published in 1902) argues that imperialism was driven by capitalism. Hobson is still a part of graduate study in IR and to a certain extent has a wider readership than Marx himself. Marx 2008 (available in many other editions and online) provides the basis for Marxist theory, but it is quite long and can be somewhat difficult to understand for the undergraduate. Lenin 1987 (available in many other editions and online) adds revolutionary fervor to Marx’s work. Kautsky 2011 (available in many other editions and online) takes it even further and argues that individual acts of terrorism, including sabotage and assassination, can help to bring about the revolution of the proletariat. Trotsky 1995 (available in many other editions and online) is a response to Kautsky that looks back to Marx (who, in turn, looked back to Hegel), arguing that individual acts are unnecessary because the revolution is inevitable. Individual acts may even delay the revolution by forcing the state to crack down on the workers. These original works are discussed in Carver 1991, which provides the reader with a wide range of ways to study, read, and understand Marx. Carver 1998 takes a postmodern approach to Marx and pays particular attention to his language and relationship to other scholars of the time.


The inclusion of neoconservatism in this article could be considered controversial for two reasons. The first is that neoconservatism is often categorized as a theory of US foreign policy rather than a theory of international relations (IR). The second is that neoconservatism has been discredited by the Iraq War, so that it is no longer necessary to include it on syllabi. Fukuyama 2007, in particular, argues that the theory needs to be reassessed in light of the failures of the Iraq War. Nevertheless, the influence of the theory on world events and the fact that it contains explicitly IR theoretical distinctions from other theories—most notably the belief that, contra realism, power provokes bandwagoning—is why it is included in this article. Muravchik 2007 does an excellent job of explaining that neoconservatives believe in morality as a basis for policy, in internationalism (something they have in common with liberal internationalists), in the efficacy of military force, and in the belief in democracy at home and abroad. There are other articles written on the domestic politics of neoconservatism, but those go beyond the scope of this bibliography. The bandwagoning versus balancing dichotomy leads to dramatic differences in policy prescriptions between theories. Mearsheimer 2005 contrasts realism and neoconservatism to argue that the classical realists, especially Hans Morgenthau, would have opposed the Iraq War. Williams 2005 presents a much more “academic” argument about how the sharp contrasts between classical realism and neoconservatism (another of which is the former’s emphasis on careful thought and gradual change, as opposed to the latter’s tendency toward bold steps) have reinvigorated the study of classical realist theory. Krauthammer 2004 calls for a “democratic realism” that has little in common with actual realism and whose name seems designed to drive realist scholars insane. Stelzer 2004 provides a wide array of selections from policymakers and thinkers, and it is useful to see some nuance in a theory often painted with broad brushstrokes and described in conspiratorial tones. The intellectual homes of neoconservatism are the American Enterprise Institute and Commentary magazine. Commentary is the single best source for the very latest in neoconservative thought, while the American Enterprise Institute’s website provides transcripts and short pieces from the leading neoconservative thinkers. The think tank itself is a place of refuge for neoconservatives when they are out of power, and since Leo Strauss’s death in 1973 it has been the intellectual center of the theory.

Feminist IR Theory

The position of feminist IR theory in the discipline has been heatedly debated, most famously between Robert Keohane (in Keohane 1998) and J. Ann Tickner (in Tickner 1997) about whether or not it is indeed a distinct theory. Keohane 1989 also takes a broad look at the contributions of feminism to international relations, though it should be noted that this is slightly different from a look at feminist IR theory per se. Weber 1994 responds to Keohane 1989 and argues that Keohane is threatened by feminist IR theory’s interdisciplinarity, and that the “feminism” he sees is not the “feminism” that is presented. This debate is at least partially the result of resistance to methodologies borrowed from other disciplines; the author of Cohn 1987, for example, uses ethnography and (a small number of) elite interviews to prove a wider point about the gendered language of the US defense establishment. Tickner 1992 attempts to present a more conventional, though nonmeta, IR theory. The author of Enloe 2014 also uses “storytelling”-like methods, but does so in a more rigorous and substantive way than Cohn 1987. Weldes and Squires 2007 attempts to put an end to this debate by delineating “gender in international relations” from “feminist international relations theory” and admonishing feminist IR theorists to stop defending themselves and get on with their research program.

Post–Cold War IR Theory

Despite the fact that the Cold War has been over for more than twenty-five years, the major IR theoretical works that were produced in the immediate wake of the Cold War continue to be studied in IR classes around the globe and they remain influential within the field. Fukuyama 1989 and Huntington 1993 are the most famous and widely read of them all. Fukuyama argues that the defeat of the Soviet Union makes the world’s progress toward free-market democracy inevitable. All states will eventually become free-market democracies, and the world will be a boring place free of both creativity and conflict. Huntington 1993 does not see the world as more peaceful. The author describes a world in which civilizations will form the primary fault lines of conflicts (though states will remain the primary actors) and argues that the West should do what it can to remain on top of “the rest.” Mearsheimer 1990 and Kaplan 1994 also produce pessimistic prognostications for the post–Cold War period. Mearsheimer argues that the forty-five years following the Cold War will likely be more violent than the Cold War itself, while Kaplan describes a near apocalyptic scenario in which the cultural and historical struggles of the future may well be too challenging for mankind to overcome. Waltz 1993 takes a middle-ground approach and argues that the emerging structure of world politics could have a variety of possible outcomes. Walt 1991 sees the end of the Cold War as opening the potential for theorists to examine broader definitions of security, but Walt argues that this broadening is a mistake and that IR theory should stick to so-called high politics. Lebow and Risse-Kappen 1995 provides a collection of nonrealist articles that aim to explain why the Cold War ended. Gaddis 1992–1993, on the other hand, tries to explain why IR theory writ large failed to predict the end of the Cold War.

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