International Relations studies interactions among states and other actors across borders — war and peace, diplomacy, foreign policy, international organizations, law, political economy, global problems, and transnational actors; states remain central, but they are not the only actors that matter. For any IR answer, first identify the level of analysis being used: individual/leadership, state/domestic, or international/systemic — many apparent theoretical disagreements are actually disagreements about which level to focus on. For every theory below, state its main actors, its core assumptions, its view of interests and power, its causal mechanism, and the kind of outcome it expects — a theory’s name is not decoration; it only becomes useful when it actually explains why a specific event occurred or why cooperation or conflict should be expected in a given case.
A. The Setting: Nation-States and International Society
The modern international system is organized mainly around territorially defined sovereign states that recognize one another as legal political units; state, nation, and nation-state are genuinely different concepts, and the system remains fundamentally decentralized — there is no world government holding the same authority over states that a state holds over its own citizens. International society describes states coexisting not merely in an anarchy of raw power, but also through shared rules, institutions, and practices — diplomacy, international law, balance-of-power practice, great-power management, and international organizations all developed over time and expanded globally through empire, decolonization, and eventually near-universal-membership institutions. The English School’s key distinction is worth mastering: an international system means simply interaction between states, while an international society means shared rules and institutions layered on top of that interaction.
B. Realism and Liberalism
Classical realism begins from power, insecurity, and conflict in a world without a central sovereign above states; classical realists such as Morgenthau connect power politics with human nature, prudence, and national interest — survival and power limit moral aspiration in this view, though realism does not claim that states always choose war. Idealism/liberal internationalism argues instead that law, institutions, democracy, economic interdependence, and shared norms can genuinely reduce conflict and support cooperation; interwar idealism emphasized collective security and international law specifically, and cooperation remains possible even under anarchy when institutions provide information, rules, and the structure for repeated interaction between states over time.
Neo-realism explains state behaviour mainly through the structure of the international system, rather than through human nature as classical realism does; Kenneth Waltz emphasizes anarchy and the distribution of capabilities among states — states seek survival, and uncertainty about others’ intentions encourages self-help and balancing behaviour, with later defensive and offensive realist variants disagreeing specifically about how much power states actually seek to accumulate. Neo-liberal institutionalism accepts anarchy and rational, self-interested states just as neo-realism does, but argues that institutions can still make cooperation meaningfully easier — institutions reduce information problems, monitor commitments, lower transaction costs, and support repeated cooperation, and in many issue areas states may care more about absolute gains (are we better off) than relative gains (are we better off than our rival), which is the central point of dispute between neo-realists and neo-liberals.
C. Constructivism, Critical Theory, Feminism, and Post-Structuralism
Behaviouralism tries to make political analysis more systematic through observable data, testable hypotheses, and empirical methods; systems analysis studies how inputs, structures, and interactions together create patterned outcomes — in IR, systemic theories focus on how the international structure affects state behaviour, while behavioural foreign-policy research studies specific decisions using measurable variables. Constructivism argues that interests and identities are actively shaped by social interaction, ideas, and norms, rather than being fixed before politics even begins; anarchy itself has different meanings depending on the relationships between the specific states involved, and norms can genuinely change what states consider legitimate or even possible over time — the changing legitimacy of colonialism, or of certain weapons, are commonly used illustrative examples.
Critical theory asks how existing international orders reproduce domination, and how these social arrangements might be transformed, rather than treating institutions and interests as neutral, given facts — it investigates historical power relations, ideology, and the possibility of emancipation, and the distinction between “problem-solving theory” (working within existing structures) and genuinely “critical theory” (questioning those structures themselves) is central to understanding its purpose. Feminism in IR examines how international politics is fundamentally gendered, and how war, security, labour, and institutions affect people differently along gender lines; it questions state-centric and heavily militarized definitions of security, and makes visible care work, sexual violence, representation, and everyday insecurity that traditional security analysis often overlooks entirely — feminism in IR is best understood as a family of approaches (liberal, critical, post-structural variants all exist) asking a shared set of questions, not as one single unified theory. Post-modern/post-structural approaches examine how language, discourse, and categories themselves produce political realities and identities, asking how concepts such as “civilized,” “threat,” or “security” are actually constructed, and whose power is strengthened by which dominant narratives — a fair criticism worth noting is that these approaches can be genuinely difficult to test empirically compared to more conventional theories.
IR Theory key takeaways: always identify the level of analysis (individual, state, or systemic) before applying any theory. Realism and liberalism disagree fundamentally about whether cooperation under anarchy is realistically achievable and sustainable. Neo-realism and neo-liberal institutionalism share rationalist, state-centric assumptions but disagree specifically about the importance of relative versus absolute gains. Constructivism, critical theory, feminism, and post-structuralism together form a family of approaches that treat interests, identities, and even security itself as socially constructed rather than simply given — and comparing what a realist, a liberal, and a constructivist would each say about the same event is one of the most reliable ways to demonstrate genuine theoretical understanding on an exam.