3 Theories of International Relations

What theories explain

International relations (IR) theories are analytical lenses. They identify which actors, forces, and processes matter most, then use them to explain outcomes such as war, cooperation, trade, and institutional change.

Because theories simplify a complex world, no single theory explains every case. Different approaches can also be combined to explain different parts of the same outcome.

A central concept is Anarchy: the international system has no world government with authority over states. Theories disagree about what this condition means for state behavior and whether institutions, shared rules, or social interaction can shape its effects.

Realism and security

Realism treats states as the principal actors in world politics. With no higher authority to guarantee their safety, states must attend to survival, security, and power. Even a state that seeks peace may worry that another state's growing military strength could become a future threat.

This uncertainty can produce competition, arms buildups, and alliances—a dynamic called the Security dilemma. For example, a realist might explain two rival states increasing defense spending as a response to uncertainty about each other's intentions, not necessarily because either has decided to attack.

Realism highlights security constraints and power politics, but may understate domestic disagreements, economic interdependence, and the possibility that identities and norms change how states interpret one another. It describes and explains power politics; it does not automatically endorse every policy pursued in the name of national interest.

Variants of realism

Realists differ over the sources and effects of competition.

• Classical realism, associated with Hans Morgenthau, relates political competition to the pursuit of power and features of human nature.

• Structural realism, also called neorealism and associated with Kenneth Waltz, explains competition chiefly through the anarchic system and the distribution of capabilities among states.

• Defensive realists stress that excessive expansion can provoke counterbalancing and undermine a state's security.

• Offensive realists argue that great powers have strong incentives to maximize their relative power.

• Neoclassical realism combines systemic pressures with domestic factors, such as leaders' perceptions and state capacity.

Liberalism and cooperation

Liberalism argues that international outcomes are shaped not only by states' security concerns but also by domestic politics, individuals, economic ties, and international institutions. Governments face internal constituencies with different interests, and democratic checks and public preferences can influence foreign policy.

Trade and other forms of Interdependence can make cooperation valuable, but they can also create vulnerability and unequal dependence.

Neoliberal institutionalism accepts that the system is anarchic and states often pursue their interests, while emphasizing that institutions can make cooperation more feasible. Institutions can provide information, establish shared rules, monitor commitments, and reduce the costs of negotiating. They do not erase competition or force states to cooperate; they can help states realize mutual gains when they have incentives to do so.

For example, states negotiating a trade agreement may create common procedures to clarify obligations and address disputes. A liberal explanation would examine expected economic gains, domestic groups that support or oppose the deal, and how its rules help sustain cooperation. Liberal approaches can illuminate cooperation, but may overestimate common interests or how well institutions constrain powerful states.

Constructivism and shared meaning

Constructivism focuses on how shared ideas, identities, norms, and expectations shape international politics. It does not claim that material factors such as weapons or wealth are unreal; it asks how actors interpret them and how social interaction gives them political meaning. State interests are not necessarily fixed: relationships, political practices, and accepted rules can shape and reshape them.

Anarchy does not dictate one single pattern of behavior. States can understand one another as enemies, rivals, or partners, and those relationships influence how they use their power. Norms can also change which actions are considered legitimate, appropriate, or unacceptable. Constructivist research often traces how understandings form, spread, and affect policy.

For example, two states may possess similar weapons but regard one another's arsenals very differently because of their histories, alliances, and expectations. A constructivist would investigate how those meanings developed and whether interaction could change them. Constructivism is especially useful for explaining shifts in identity, norms, and political legitimacy; by itself, it may offer less precise predictions about when material pressures will override social expectations.

Approaches beyond the main three

Several important traditions broaden IR analysis beyond realism, liberalism, and constructivism. They often ask questions that leading state-centered theories give less attention to.

• The English School examines how states form an international society. Without a world government, states may still share rules and institutions, including diplomacy, international law, and practices that help maintain order. This approach connects realist attention to power with liberal and constructivist attention to rules and social relations.

• Marxist and critical approaches study how capitalism, class, labor, and historical structures distribute wealth and power. They ask how global economic arrangements benefit some groups while constraining others, and how those arrangements might be transformed.

• Feminist IR examines how gendered roles and assumptions shape power, security, war, political representation, and whose experiences count as internationally significant. It asks not only where women are in world politics, but also how ideas about gender influence institutions and policy.

• Postcolonial approaches trace how empire and colonial histories continue to shape global hierarchies, knowledge, and economic and political relationships. They question whose experiences conventional accounts center and how colonial categories and inequalities persist after formal colonial rule.

• Poststructuralist approaches analyze how language and political narratives shape the categories through which problems are understood, such as how leaders define a threat, an identity, or a legitimate use of force. They examine how these representations enable some policies and marginalize others.

These are broad families of thought, not single, uniform theories. They also differ in their goals: some primarily aim to explain outcomes, while critical approaches more explicitly examine power, inequality, and possibilities for change.

Comparing explanations

Consider a hypothetical decision by neighboring states to form a security pact. Each approach directs attention to different questions:

• Realism: What threat prompted the pact, and how does it shift the balance of power?

• Liberalism: What shared interests and institutional arrangements support cooperation, and which domestic groups favor it?

• Constructivism: How do the states' identities and shared expectations shape whom they see as a threat or partner?

• The English School: Which shared rules or diplomatic practices help make the pact part of a wider international order?

• Marxist or critical approaches: Whose material interests does the pact serve, and how are its costs and benefits distributed?

• Feminist or postcolonial approaches: Whose security experiences and historical perspectives are included or excluded from the pact's definition of security?

The approaches can complement one another. A security pact may arise from a perceived military threat, become workable through institutional coordination, and be reinforced by a shared identity. Which account is most useful depends on the question, evidence, and level of analysis.

Bringing the lenses together

Realism explains international outcomes through anarchy, power, and the pursuit of security. Liberalism emphasizes domestic preferences, interdependence, and institutions that can facilitate cooperation. Constructivism explains how identities, norms, and shared meanings shape interests and behavior.

The English School, Marxist and critical approaches, Feminist IR, Postcolonial approaches, and Poststructuralist approaches broaden analysis by emphasizing international society, economic structures, gender, colonial legacies, and political narratives. Comparing these lenses helps explain not only what happened, but why theories identify different causes and consequences.