Liberalism is a school of thought in international relations theory holding that the prospects for cooperation, peace, and progress among states are substantially better than rival traditions suggest, owing to the influence of domestic political institutions, economic interdependence, and international organizations and law. It stands alongside realism and constructivism as one of the major paradigms through which scholars and policymakers interpret state behavior. Liberalism is not a single unified theory but a family of related arguments, and the term itself is sometimes used differently by different authors; see liberalism-international-relations-definition-debate for disagreement over how the term should be bounded.

Contemporary liberal international relations theory is generally organized around several core strands rather than a single master argument. Republican (or democratic peace) liberalism holds that democratic states are less likely to go to war with one another, though scholars continue to dispute the causal mechanism and the robustness of the empirical pattern. Commercial liberalism argues that economic interdependence, particularly trade, raises the costs of conflict and creates incentives for cooperation. Institutional (or neoliberal) liberalism, closely associated with neoliberal institutionalism, contends that international institutions and regimes can mitigate the anarchic structure of the international system emphasized by realists by reducing transaction costs, increasing transparency, and enabling iterated cooperation. Sociological and ideational variants emphasize transnational ties, norms, and non-state actors as additional channels shaping state behavior.

Liberal theory is frequently discussed in contrast with structural realism, which treats the international system as anarchic and states as primarily security-seeking, skeptical of the possibility of durable cooperation. Liberalism is also distinguished from constructivism, which focuses on the role of shared ideas, identities, and norms in constituting state interests rather than treating institutions or interdependence as exogenous causal variables. Since the late twentieth century, much liberal scholarship has proceeded through close engagement and synthesis with both rival traditions, including hybrid approaches such as liberal institutionalism's debates with neorealism over the durability of cooperation under anarchy. A fuller account of liberalism's development is treated separately. See liberalism-international-relations-history.

• Democratic peace liberalism holds that the absence of war between mature democracies is a robust empirical regularity explained by domestic institutional constraints, shared norms, or transparency between democratic states. See liberalism-international-relations-democratic-peace-viewpoint.
• Commercial liberalism holds that trade and economic interdependence reduce the likelihood of interstate conflict by raising its opportunity costs and creating cross-border constituencies favoring peace. See liberalism-international-relations-commercial-viewpoint.
• Institutional (neoliberal) liberalism holds that international institutions and regimes enable sustained cooperation among self-interested states even under anarchy, by lowering transaction costs and facilitating information-sharing. See liberalism-international-relations-institutional-viewpoint.
• Republican liberalism emphasizes the internal constitutional and representative character of states as the primary determinant of their international conduct, distinguishing it from purely behavioral accounts of democratic peace. See liberalism-international-relations-republican-viewpoint.
• Realist-skeptical viewpoint holds that liberal claims about cooperation, interdependence, and institutions understate the persistence of power competition and the constraints of anarchy emphasized by structural realism. See liberalism-international-relations-realist-skeptical-viewpoint.
• Constructivist-critical viewpoint holds that liberalism's reliance on fixed, rationalist assumptions about state interests neglects the socially constructed nature of those interests, a critique developed within constructivism. See liberalism-international-relations-constructivist-critical-viewpoint.
• Critical and postcolonial viewpoint holds that liberal international relations theory, including its emphasis on democracy promotion and free trade, reflects and has historically reinforced Western and great-power interests. See liberalism-international-relations-critical-viewpoint.

• The empirical robustness and causal interpretation of the democratic peace thesis has been the subject of sustained scholarly dispute, including disagreement over case selection and statistical methodology. See liberalism-international-relations-democratic-peace-controversy.
• The relationship between economic interdependence and conflict, including whether trade reliably pacifies relations between great powers, remains contested. See liberalism-international-relations-interdependence-conflict-controversy.

• liberalism-international-relations-history
• liberalism-international-relations-definition-debate
• liberalism-international-relations-democratic-peace-controversy
• liberalism-international-relations-interdependence-conflict-controversy
• Structural Realism
• Constructivism (International Relations)

1. Robert O. Keohane and Joseph S. Nye, *Power and Interdependence*, 4th ed. (Boston: Longman, 2012).
2. Michael W. Doyle, "Liberalism and World Politics," *American Political Science Review* 80, no. 4 (1986): 1151-69.
3. Robert O. Keohane, *After Hegemony: Cooperation and Discord in the World Political Economy* (Princeton: Princeton University Press, 1984).
4. Andrew Moravcsik, "Taking Preferences Seriously: A Liberal Theory of International Politics," *International Organization* 51, no. 4 (1997): 513-53.
5. John J. Mearsheimer, "The False Promise of International Institutions," *International Security* 19, no. 3 (1994/95): 5-49.