What realism claims
Realism is the oldest and most influential tradition in the academic study of international relations. Its central claim is simple: international politics is a contest for power among states that exist in a condition of anarchy — a system with no central authority to enforce rules or guarantee survival. Because states cannot rely on anyone else for their security, they must provide for it themselves, and this self-help logic pushes them to maximise power and to be wary of the intentions of others.
Three assumptions do the heavy lifting:
- Statism. States are the principal actors. International organisations, corporations, NGOs and individuals matter, but their influence runs through states and their interests.
- Survival is the first goal. Before states pursue wealth, ideology or prestige, they must survive. Every other objective is secondary to security.
- Anarchy is the ordering principle. There is no world government. The absence of a final arbiter means that promises can be broken with impunity, and therefore commitments are credible only when backed by power or interest.
Classical realism: human nature
Classical realism, associated with Thucydides, Niccolò Machiavelli and Hans Morgenthau, locates the drive for power in human nature. Morgenthau argued that homo politicus seeks power the way homo economicus seeks wealth — not as a means but as a disposition. Politics is therefore an autonomous sphere with its own logic: the pursuit of interest defined as power.
The Athenian argument in the Melian Dialogue is the canonical statement: “The strong do what they can and the weak suffer what they must.”
Neorealism: the structure of the system
Kenneth Waltz’s Theory of International Politics (1979) shifted the explanation from human nature to the structure of the system. For Waltz, outcomes are explained by the distribution of capabilities — unipolarity, bipolarity or multipolarity — not by the personality of leaders. Anarchy constrains even well-intentioned states: because the system rewards power and punishes weakness, states that behave peacefully but cannot defend themselves invite predation.
Structural realism’s predictions are spare but powerful: balancing will recur; alliances are marriages of convenience; international institutions are tools of the powerful rather than independent constraints.
Offensive vs defensive realism
The neorealist school splits over how much power states want:
- Defensive realism (Waltz, Stephen Walt, Robert Jervis) holds that states seek security, not hegemony. Because aggression is costly and usually self-defeating, states balance and stop when they are safe. The international system is “benign” in the sense that status-quo behaviour is survivable.
- Offensive realism (John Mearsheimer) holds that states can never be certain how much power is enough, so great powers want to be the strongest in their region, and prefer hegemony to equilibrium. The system is “brutal”: great powers are always searching for opportunities to shift the balance of power in their favour.
What realism explains — and what it misses
Realism performs well on the questions it sets out to answer: why wars recur, why balances of power form, why alliances shift, why cooperation breaks down when relative gains matter. Its weaknesses are equally well documented. It struggles to explain large areas of international life where cooperation is durable and independent of power — the European Union, the postwar trading order, the ban on nuclear weapons — which is the empirical terrain of liberalism, constructivism and institutionalist theory. It also underweights domestic politics, identity and ideas, which constructivists argue shape what states want in the first place.
Reading list
- Thucydides, History of the Peloponnesian War (Melian Dialogue, Book V)
- Hans J. Morgenthau, Politics Among Nations (1948)
- Kenneth N. Waltz, Theory of International Politics (1979)
- Robert Gilpin, War and Change in World Politics (1981)
- John J. Mearsheimer, The Tragedy of Great Power Politics (2001)
