International Relations Theories

International Relations theories explain why states and other actors cooperate, compete, fight, build institutions and contest rules. The field includes realist and liberal traditions. It also covers functionalist, Marxist, constructivist and post-positivist traditions. The English School and later variants such as Neorealism and Neoliberalism add further ways to organize the debate.

Summary

• Realism emphasizes power, security and anarchy.
• Liberal and neoliberal theories emphasize cooperation, institutions and interdependence.
• Constructivism and post-positivist approaches examine identities, norms, discourse and the assumptions behind theory itself.

Liberalism

Liberalism emerged as a significant school of International Relations in the 20th century. One of its central tenets is that a state’s security depends on the security of other states. According to liberals, states are rational actors capable of using reason to achieve mutually beneficial cooperation. Liberalism therefore treats world affairs as a possible positive-sum game. Cooperation can improve the position of several actors at the same time.

Several factors contribute to this cooperative international environment:

• Free Trade: Liberals argue that free trade fosters interdependence among nations. Through trade, countries exchange goods and services, benefiting economically and creating a network of mutual dependencies that reduce the likelihood of conflict.
• Democracy: Democratic nations are believed to be more peaceful in their interactions with other democracies, a concept known as the “Democratic Peace Theory”. This theory suggests that democratic norms and institutions promote peaceful conflict resolution.
• International Institutions: Institutions such as the United Nations play a crucial role in fostering cooperation and resolving disputes. These institutions establish norms and rules that guide state behavior, making international relations more predictable and stable.

Key figures shaped the principles and arguments of Liberalism. Norman Angell wrote The Great Illusion in 1910. He argued that war was economically and socially irrational, because both victors and losers suffer its consequences. Woodrow Wilson put forward the “Fourteen Points” after World War I. That program aimed to create a framework for stable and lasting peace.

Realism

Realism in International Relations emerged during the interwar period as a reaction to the perceived failures of Liberalism, especially after World War I. It gained major prominence during the Cold War. Realism offers a stark view of international politics, emphasizing power and competition among states.

Realists argue that the international system is anarchic. It is composed of sovereign states with no overarching authority above them. Drawing from Thomas Hobbes, realists maintain that the world exists in a state of nature marked by insecurity and potential conflict. States act in their self-interest and must provide for their own security. According to most realists, international interactions are zero-sum games, particularly in matters of security. Robert Jervis challenged this view by arguing that states can cooperate on security when they choose to do so.

Edward Carr criticized liberals for their naive belief in principles and institutions, arguing that principles are subordinate to politics. Hans Morgenthau defined state interests in terms of power. For him, power included military capacity, economic resources and political influence. John Herz introduced the concept of the “security dilemma”. It describes how one state’s defensive measures can look threatening to others, producing arms races and broader insecurity.

Learn more about Classical Realism in International Relations.

Functionalism

Functionalism emerged in the 1930s, primarily through the work of David Mitrany. He criticized state borders as obstacles to a global society. Mitrany proposed a system of international agencies that would take over selected functions traditionally held by states. These agencies would promote cooperation first in “low politics”, especially economic and social issues. Security and defense would remain harder areas for integration.

Proponents of Functionalism study specialized international organizations and the gradual building of “peace by pieces”. A critical aspect of this theory is the spill-over effect. It means that successful cooperation in one area can extend to other areas and encourage further cooperation. In The Uniting of Europe (1958), Ernst Haas showed how cooperation in coal, steel and nuclear research helped European integration. Karl Deutsch also studied regional integration initiatives.

The English School

The English School emerged primarily from the British Committee on the Theory of International Politics, established in 1959. It draws on law, philosophy, history and sociology.

The English School proposes a middle way between Realism and Liberalism, called Rationalism. From Realism, it adopts the concept of anarchy. From Liberalism, it borrows the idea that cooperation is possible and essential. This combination lets the English School argue that systemic and normative factors shape state behavior even under anarchy. Rules and shared expectations can support stable coexistence among states with different national interests.

Scholars associated with this school describe several stages of relations among states. At one end is an international system, where states interact despite having little in common. At the other is a world government, where a supranational entity imposes governance from above. According to Adam Watson, Europe stands in the middle of this continuum because it has an international society. Its states share customs, norms, principles and values.

Both Martin Wight and Hedley Bull are key thinkers within the English School. Wight is known for segmenting IR theory into three traditions, known as the “three Rs”: Revolutionism, Realism and Rationalism. Bull argued that a stable international system is a prerequisite for achieving international justice and for upholding principles like self-determination and state sovereignty.

Neorealism

Neorealism, also known as Structural Realism, emerged as a response to the perceived limits of Classical Realism. Classical Realism links the pursuit of power to human nature. Neorealism places the cause in systemic constraints.

Kenneth Waltz is the principal figure behind Structural Realism. In Man, the State, and War (1959), he argued that war can be explained through individual, state and systemic levels of analysis. In Theory of International Politics (1979), he linked war to international anarchy. For Waltz, states are rational and self-interested actors that react against any state trying to maximize its power. He considered bipolar orders more transparent, stable and predictable than multipolar systems.

Waltz’s theory, known as Defensive Realism, contrasts with John Mearsheimer’s argument in The Tragedy of Great Power Politics (2001). Mearsheimer argued that the best strategy for national survival is power maximization. However, he conceded that global hegemony might be difficult to achieve. He therefore argued that states should pursue regional hegemony and delegate distant matters to other regional powers, a process called “buck-passing”.

Neoliberalism

In the 1950s and 1960s, liberal theories struggled to counter the dominance of Realism within International Relations. In the 1970s, Robert Keohane and Joseph Nye introduced Neoliberalism. The approach is also called Institutional Liberalism. It emerged in the context of Cold War détente. Keohane and Nye argued that security was giving way to other topics in international politics. These included human rights, economic development, environmental concerns and geopolitical non-alignment. Neoliberalism claimed that Neorealism neglected these “low politics” issues and underestimated domestic variables and non-state actors.

The most important concept for neoliberals is that of “complex interdependence”. This idea asserts that in the modern world, the actions of an actor invariably affect others. In particular, there were three characteristics of the modern world that made states and non-state actors interdependent:

• Multiple channels of contact among societies, because there emerged relationships between states, international organizations, NGOs and individuals.
• Lack of clear hierarchies of issues, because economic, social, environmental, and other kinds of issues exist and one kind does not prevail over the others.
• Irrelevance of military force, because it is largely irrelevant in non-military disputes between countries, such as trade disputes.

A world characterized by complex interdependence is a world where states face increased risks, because everything is interconnected. According to Keohane and Nye, international cooperation is a viable strategy for managing those shared risks. Since interdependence affects states similarly, they have a vested interest in common solutions. The 1973 Oil Crisis offers one example: developed countries joined forces to counter price hikes organized by OPEC. Practical economic pressure drove that cooperation.

Neoclassical Realism

Neoclassical Realism was introduced by Gideon Rose in 1998. Like Neorealism, this theory maintains that the international system is the primary level of analysis. However, unlike Neorealism, Neoclassical Realism acknowledges that domestic variables can significantly influence state behavior. In particular, scholars that adopt this approach believe that a state’s foreign policy can be explained by systemic variables (material capabilities), cognitive variables (interpretations) and domestic variables. The latter include domestic political institutions, the preferences of the elites, and social ideologies.

Stephen Walt, William Wohlforth and Randall Schweller are among the authors associated with this approach. Daniel Deudney, Fareed Zakaria and Jeffrey Taliaferro are also important names in the debate. These authors criticize the oversimplifications of Neorealism and provide a compelling alternative for moving beyond the model of states as “black boxes”.

Marxism

Marxism in International Relations is a theoretical framework that employs historical materialism to analyze how the material conditions of production determine social organization and development. Karl Marx and Vladimir Lenin saw capitalism as a force that could modernize traditional societies and economies. Marxist scholars of IR emphasize another effect: capitalism generates economic disparities and exploitative relations between states. Multinational corporations often capture the benefits of these relations.

A prominent Marxist scholar of IR was Immanuel Wallerstein, who introduced the “World-System Theory”. He divided states into core, semi-periphery and periphery. According to him, the core is made up of developed countries. These countries dominate the means of production and produce high-value-added goods. They also exploit both the semi-periphery and the periphery. The periphery contains the most exploited countries. The semi-periphery occupies an intermediate position, because it exploits the periphery while being exploited by the core. In contrast to the core, both of them produce primary goods, which are less profitable.

Marxist scholars who adopt the “Dependency Theory” claim that the poor get poorer while the rich get richer. The reason is unequal exchange: primary goods exported by the periphery and semi-periphery do not compensate for the industrialized goods they import. In line with Marxism, these authors argue that the contradictions inherent in capitalism will deepen its crises and ultimately cause its collapse.

Constructivism

Constructivism was introduced to International Relations in the 1980s. It gained prominence in the following decade, because it helped explain the end of the Cold War. It also addressed the increasing importance of individuals in global affairs. This approach contends that ideas, rules and institutions are crucial for understanding state behavior and the dynamics of the international system.

Drawing from Anthony Giddens’ Theory of Structuration, constructivists argue that agents and structures co-constitute each other. In other terms, the international system does not fully determine how states behave. The behavior of individual states also does not fully determine how the international system evolves. Rather, the identities and interests of states are socially constructed and can change over time. For this reason, constructivists criticize the emphasis that Realism places on military capabilities. For instance, a state might feel more threatened by an enemy with one nuclear warhead than by an ally with many. This shows that social meanings, rather than mere material capabilities, influence the actions of states.

Leading constructivists within International Relations are Alexander Wendt, Nicholas Onuf and Friedrich Kratochwil:

• Wendt was the first constructivist within IR. He introduced the notion of the “cultures of anarchy”, which consist of possible scenarios for the international system: conflict (Hobbesian culture), rivalry (Lockean culture), or cooperation (Kantian culture) between states. According to him, “Anarchy Is What States Make of It”, meaning that states are free to strive for any possible culture of anarchy, instead of condemned to a single one of them at all times.
• Onuf went beyond the legacy of Wendt by emphasizing the role of conventions, norms, rules and international institutions in shaping state behavior. According to him, conventions are behaviors that states adopt because they have traditionally done so, and norms and rules are behaviors that states adopt because they believe they are required to do so. Both constrain state action, but, because they are socially constructed, they are subject to change over time.
• Kratochwil revolutionized Constructivism as a meta-theory of International Relations, because he broke with “Positivist” assumptions that both Wendt and Onuf made, to a certain extent. He argued that the only limits to the actions of states were intangible limits, such as linguistic norms and socially constructed rules. However, he did concede that such limits are somewhat hard to change, because they are based upon social consensus and practical considerations.

Post-Positivism

Post-Positivist theories of International Relations emerged as a critical response to Positivism, which was the mainstream meta-theoretical approach within the discipline until a few decades ago. Positivists hold that scientific knowledge can be neutral and verifiable, especially if it employs methods from the natural sciences. On the other hand, post-positivists contend that science cannot provide an objective view of reality. Scientists have biases, and their language is not neutral. Their methods are also imperfect in the social sciences, because social phenomena cannot be studied in isolated lab conditions.

There are several strands of Post-Positivism in IR, such as:

• Critical Theories: They were influenced by the Frankfurt School, a sociological approach that blends Marxism, psychoanalysis and empirical sociological research. Key proponents of these theories are Andrew Linklater and Robert Cox, who criticize the fact that a handful of powerful states control the international system.
• Poststructuralist Theories: Also called “Postmodern Theories”, they argue that language, perceptions, and cognitive processes significantly shape the observation and analysis of social phenomena. They were influenced by thinkers such as Friedrich Nietzsche, Jacques Derrida, and Michel Foucault. Within IR, R.B.J. Walker is an important poststructuralist author, with several works that are critical of “us versus them” discourses.
• Postcolonial Theories: They criticize the Eurocentric character of modern international relations and the fact that certain countries and societies remain subjugated, despite having achieved political independence. Edward Said, for instance, famously denounced Western portrayals of Eastern people in a patronizing way.
• Feminist Theories: They argue that International Relations predominantly focus on masculine themes and ideas, while women and their feminine traits are neglected. Against this chauvinist tendency, for example, Cynthia Enloe emphasized the role of women in international politics, both within states and within private entities such as multinational corporations and NGOs.
• Queer Theories: They argue that IR scholars fail to account for the ideas, needs and perspectives of non-binary people, considering them as deviations from gender and sexuality standards. A key proponent of these theories within the discipline is Cynthia Weber, who condemned the heterosexual traits of the international system since the Peace of Westphalia.

Conclusion

Theories of International Relations offer different ways to read global politics. Liberal approaches emphasize cooperation and interdependence. Realist approaches focus on power and anarchy. Functionalism and the English School ask how institutions, rules and shared expectations can sustain order. Marxism highlights the economic inequalities produced by capitalism. Constructivism examines how social meanings shape state behavior. Post-positivist approaches challenge traditional paradigms and push the field to include voices that older theories often excluded. Together, these theories help explain how states and non-state actors interact in a complex international system.