The study of International Relations (IR) encompasses a broad array of theories that provide diverse perspectives on how states interact, the nature of the international system, and the factors influencing global politics. Each theory has its own assumptions and provides its own insights about state behavior and global governance. As an academic field of study, IR began with liberal theories in the context of World War I. Later on, liberal thought would be countered by various strands of Realism (such as Classical Realism, Neorealism and Neoclassical Realism) and would be reinforced by various strands of Liberalism (such as Functionalism and Neoliberalism). The English School emerged as an alternative to both liberal and realist thought, and, in the last decades of the twentieth century, many more theories emerged. Through these varied lenses, scholars can better understand the complexities of global interactions and the multifaceted nature of international affairs. This article provides an overview of the most relevant theories of IR, their proponents and their arguments.
Liberalism
Liberalism emerged as a significant school of International Relations in the 20th century. One of its central tenets is the idea that a state’s security can only be assured when the security of all states is guaranteed. According to liberals, states are rational actors capable of using reason to achieve mutually beneficial cooperation. Unlike realism, which views international politics as a zero-sum game driven by power struggles, liberalism posits that world affairs can be a positive-sum game where cooperation leads to win-win scenarios.
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, arguing that war was economically and socially irrational, because both victors and losers suffer its detrimental consequences. Woodrow Wilson, the former U.S. president, put forward the “Fourteen Points” after World War I, a series of liberal principles aimed at establishing a framework for a stable and lasting peace.
Realism
Realism in International Relations emerged during the interwar period as a reaction to the perceived failures of Liberalism, particularly following the outbreak of World War I. Gaining significant prominence during the Cold War, Realism offers a stark, pragmatic view of international politics, emphasizing the enduring role of power and the competitive nature of state interactions.
Realists argue that the international system is anarchic, meaning it is composed of sovereign states with no overarching authority above them. Drawing from the ideas of Thomas Hobbes, realists maintain that the world exists in a perpetual state of nature characterized by insecurity and potential conflict. In this arena, states are seen as rational actors that operate in their self-interest. They cannot rely on other states for security, leading to a system of self-help where each state must ensure its own safety. According to most realists, international interactions are zero-sum games, particularly in matters of security — that is, the gain of one state often comes at the expense of another. Robert Jervis argued against this view, stating that states are able to cooperate in matters of security if they choose to do so.
Major scholars associated with Realism are Edward Carr, Hans Morgenthau, and John Herz. Carr criticized liberals for their naive belief in principles and institutions, arguing that principles are subordinate to politics. Morgenthau emphasized that the interests of states are defined in terms of power, but claimed that power has multiple dimensions: military, economic, political, etc. John Herz introduced the concept of “security dilemma”, according to which actions taken by a state to ensure its own security can be perceived as threats by other states, leading to arms races and increased insecurity for everyone.
Learn more about Classical Realism in International Relations.
Functionalism
Functionalism emerged in the 1930s, primarily advanced by David Mitrany. He criticized the notion of state borders, viewing them as major obstacles to forming a global society. He proposed that nation-states should be replaced by a system of international agencies. These agencies would be permanently assigned some of the functions and authority traditionally held by states, fostering cooperation, especially in areas of “low politics”, such as economic and social issues, rather than “high politics”, which involve matters of security and defense.
Proponents of Functionalism focus on studying the operation of specialized international organizations, fostering international cooperation in a way that would ensure “peace by pieces”. A critical aspect of this theory is the spill-over effect, which posits that successful intergovernmental cooperation in one area would extend to other areas, encouraging further cooperation. For instance, in “The Uniting of Europe” (1958), Ernst Haas analyzed how cooperation in areas like coal, steel, and nuclear research facilitated European integration through spill-over effects. Other authors associated with Funcionalism are Karl Deutsch and David Mitrany, who 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, and draws on a rich array of influences from disciplines such as 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, recognizing that there is no overarching authority above sovereign states. From Liberalism, it borrows the notion that cooperation is possible and essential in international relations. This combination enables the English School to argue that systemic and normative factors — such as rules, norms, values, principles, decision-making processes, and behavior patterns — significantly influence state behavior, even within an anarchic international system. These factors enable stable coexistence among states, despite the fact that they have different national interests.
Scholars associated with this school posit that there are several stages of international relations among states, beginning with an international system (in which states interact despite having little in common) and ending with a world government (a supranational entity that imposes governance from above). According to Adam Watson, Europe stands at the middle of this continuum, because there is a European international society: an integrated set of states that 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 limitations of Classical Realism. Unlike the latter, which attributes the pursuit of power to human nature, the former argues that systemic constraints in the international system drive states to seek power.
Kenneth Waltz is the principal figure behind Structural Realism. In “Men, the State, and War” (1959), he was influenced by behaviorists and claimed that the phenomenon of war can be explained through three levels of analysis: the individual level, the state level, and the systemic level. In “Theory of International Politics” (1979), he posited that war is explained by international anarchy, which is immutable — that is, no state can ever become an hegemonic power. According to Waltz, states are rational and self-interest actors that try to maintain a balance of power, reacting against any state that tries to maximize its own power at the expense of the others. He believed that the best balance of power was that within a bipolar order, considered as more transparent, stable, and predictable than multipolar systems.
Waltz’s theory, known as Defensive Realism, contrasts with the ideas of another neorealist, John Mearsheimer, in the book “The Tragedy of Great Power Politics” (2001). Mearsheimer argued that, in the face of international competition for national survival, the best strategy is for a state to maximize its own power. However, he conceded that global hegemony might be difficult to achieve, thus he proposed that a state should strive for regional hegemony, and delegate matters outside its own vicinity 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, or Institutional Liberalism, in the context of the détente of the Cold War. These scholars realized that security issues were giving way to other topics within international politics, such as human rights, economic development, environmental concerns and geopolitical non-alignment. Neoliberalism claimed that Neorealism neglected these “low politics” issues and failed to account for the impact of domestic variables and non-state actors in international relations.
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, more than being a path for achieving world peace, international cooperation is a viable strategy for managing the challenges of interdependence. Since interdependence affects states similarly, they have a vested interest in finding common solutions to shared problems. An example of this was the 1973 Oil Crisis, when developed countries joined forces to counter price hikes that had been organized by the OPEC. This cooperation did not stem from an imperative desire for peace but from practical considerations to address a pressing economic issue.
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.
Some of the authors that adopt this approach are Stephen Walt, William Wohlforth, Randall Schweller, Daniel Deudney, Fareed Zakaria and Jeffrey Taliaferro. They 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. Although Karl Marx and Vladimir Lenin believed that capitalism had a modernizing and civilizing effect on traditional societies and economies, Marxist scholars of IR posit that capitalism generates economic disparities and exploitative relations between states. Often, multinational corporations are the ones that benefit from these relations, rather than states.
A prominent marxist scholar of IR was Immanuel Wallerstein, who introduced the “world-system” theory. He categorized states into three groups: the core, the semi-periphery and the periphery. According to him, the core is comprised of developed countries, which dominate the means of production, produce high-value-added goods, and exploit both semi-periphery and periphery. The periphery is comprised of the most exploited countries, while the semi-periphery is in a better position, exploiting 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, because primary goods exported by the periphery and semi-periphery do not compensate for the industrialized goods imported by them. In line with Marxism, these authors argue that the contradictions inherent in capitalism will lead to increasingly deep crises, ultimately causing its collapse.
Constructivism
Constructivism was introduced to International Relations in the 1980s and gained prominence in the following decade, as it properly explained the end of the Cold War and the increasing importance of individuals in global affairs. This approach contends that ideas, rules, and institutions are crucial for understanding both the behavior of states and the dynamics of the international system.
Drawing from Anthony Giddens’ Theory of Structuration, constructivists argue that both agents and structures co-constitute each other. In other terms, the international system does not determine how states will behave, and the behavior of individual states does not determine how the international system will evolve. Rather, the identities, interests and actions of states are socially constructed and can change over time. For this reason, constructivists decry the emphasis that Realism places on the military capabilities of states. For instance, a state might feel more threatened by an enemy with a single nuclear warhead than by an ally with many. This proves that social meanings, rather than mere material capabilities, are responsible for influencing 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 the methods from the natural sciences. On the other hand, post-positivists contend that science cannot provide an objective view of reality, because scientists are biased, their language is not neutral, and their methods are imperfect — particularly in the social sciences like IR, 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
The diverse theories of International Relations each contribute unique perspectives and methodologies to understanding global politics. Liberalism and Neoliberalism emphasize cooperation and interdependence, advocating for democratic principles and international institutions. Realism and its derivatives focus on power dynamics and the anarchic nature of the international system. Meanwhile, Functionalism proposes a more integrated global society through specialized agencies, and the English School balances the realist and liberal views, highlighting the importance of norms and rules. Marxism critiques the economic disparities perpetuated by capitalism, and Constructivism underscores the social constructs shaping state behavior. Post-positivist approaches, including Critical, Poststructuralist, Postcolonial, Feminist, and Queer theories, challenge traditional paradigms, advocating for the inclusion of diverse voices and perspectives. Together, these theories provide a comprehensive framework for analyzing international relations, enabling a deeper understanding of the complexities of global interactions among states and non-state actors.
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