Plain-language explanation.
International relations (IR) theory tries to explain why countries behave as they do on the world stage. Why do wars start? Why do countries cooperate? Why do some nations dominate? Realism says countries are self-interested power-seekers in an anarchic world. Liberalism says institutions and trade create cooperation. Constructivism says identities and ideas shape what states want in the first place.
Core concepts and standard treatment.
Major IR theoretical traditions: realism (Morgenthau, Waltz, Mearsheimer) — states are unitary rational actors in an anarchic system; power is the primary currency; security dilemma (states arming for defence appear threatening, triggering arms races); structural realism (neorealism) argues the international system's structure, not human nature, drives state behaviour — distribution of power determines outcomes; offensive vs. defensive realism. Liberalism (Kant, Keohane, Nye) — democratic peace theory (democracies do not fight each other); international institutions reduce uncertainty and promote cooperation; complex interdependence (multiple channels, no hierarchy of issues, military force less usable). Constructivism (Wendt, Finnemore) — "anarchy is what states make of it"; interests and identities are socially constructed through interactions; norms, rules, and ideas shape state behaviour — not just material power.
Deeper theory, debates and edge cases.
Critical IR theories: English School (Bull, Wight) — international society as a middle ground between anarchy and world government; institutions (balance of power, diplomacy, international law, war, great powers) maintain order; solidarism vs. pluralism on humanitarian intervention. Feminist IR (Tickner, True) — how gender hierarchies shape world politics; women's experiences in conflict, development, and diplomacy are systematically marginalised. Post-colonialism (Fanon, Said, Acharya) — IR theory reflects Western/Eurocentric assumptions; non-Western states have different historical experiences and interests; the "discovery" narrative of international society ignores colonial violence. Neo-Gramscian and critical theory (Cox) — global order reflects the interests of hegemonic classes; international institutions serve dominant powers; counter-hegemonic coalitions.
How it is applied in practice.
IR theory in policy analysis: structural realist framework in US-China competition (Mearsheimer's "Tragedy of Great Power Politics" — rising powers inevitably challenge hegemons, predicting conflict); liberal institutionalist argument for maintaining WTO, WHO, and other institutions even under stress (Ikenberry's "After Victory" — hegemonic order-building through institutions); constructivist analysis of norm cascades (Finnemore and Sikkink) — how norms like anti-slavery, women's suffrage, and R2P spread through international society. Quantitative IR: Correlates of War project, Militarised Interstate Disputes (MID) dataset, and statistical testing of IR hypotheses (democratic peace, power transition, trade and conflict). The IR theory-policy gap: academic IR theories and the frameworks that policymakers actually use often diverge — area expertise, analogical reasoning, and organisational culture shape foreign policy more than explicit theory.