States are the dominant actors operating in anarchy, pursuing national interest defined as security and power, unable fully to trust one another, with war a recurring feature.
Realism treats states as the dominant actors, billiard balls colliding in anarchy. It does poorly on non-state actors such as multinationals, NGOs and terrorist groups, which realists tend to call anomalies.
For neo-realism the real driver is structure: anarchy forces any state, whatever its regime type, to balance and pursue security. Anarchy is the bedrock condition that shapes how states behave.
Realism holds that cooperation is possible but limited and contingent on the balance of power. States cannot trust one another because there is no enforcement of agreements above them, and war remains a recurring feature.
Realism does poorly on the EU, the WTO and the ICJ. Realists usually treat institutions that constrain great powers as anomalies, marginal cases, or the products of underlying power rather than genuine constraints.
Classical realism (Morgenthau, 1948) roots behaviour in a Hobbesian, power-seeking human nature. Neo-realism (Waltz, 1979) rejects that and points to structure instead, so the tradition is split on this claim.
Realism explains behaviour through security, power and the balance of power, not identity. Critics note realism cannot explain identity-driven patterns such as post-1945 German or Japanese pacifism.
Cooperation is possible and durable; states are not the only actors; institutions, interdependence and democratic peace tame anarchy.
Liberalism holds that states are not the only actors: international institutions, NGOs and multinational corporations all shape outcomes. This is a direct rejection of the realist billiard-ball picture.
For liberalism anarchy does not dictate behaviour: states can build institutions that bind themselves, and trade interdependence raises the cost of war. Anarchy does not prevent durable cooperation.
Liberalism holds that cooperation is possible and durable. Institutions reduce the costs of cooperation and build trust, complex interdependence raises the cost of war, and democracies rarely fight one another.
Neoliberal institutionalism (Keohane) argues institutions reduce transaction costs, build reputation and monitor compliance. The WTO, EU, NATO and the Paris ratchet are read as genuine constraints on great powers.
Liberalism rejects the pessimistic frame: the international order is improvable through law, trade and the spread of democracy. Kant's Perpetual Peace argued war would diminish as states became republics.
Democratic peace theory makes regime type and shared democratic norms matter, which leans ideational, but liberalism mainly explains cooperation through material mechanisms such as institutions and trade interdependence.
There is more order in international politics than realists admit, because states form a society of states sharing norms, rules and institutions. Order coexists with anarchy.
The English School is built around a society of states sharing rules of sovereignty, diplomacy and non-intervention. Critics argue its focus on states underweighs non-state actors and economic globalisation.
The English School accepts the realist premise that international politics is anarchical, but argues it is also a society. Order coexists with anarchy because states share norms, so anarchy alone does not dictate behaviour.
The English School sees real international order resting on consent and shared understanding. Coordinated sanctions on Russia look like a society of states punishing a rule-breaker, not just power politics.
Bull identified five institutions of the society of states: balance of power, international law, diplomacy, war as a regulated practice, and great-power management. Norms shape behaviour even when states violate them.
The English School argues international society is different from a Hobbesian state of nature: shared norms, rules and a sense of common interests make it more ordered than a grim view of human nature implies.
Shared norms, rules and mutual recognition do real work for the English School, which is partly ideational. But it remains state-centric and rooted in the institutions of a society of states rather than identity.
Identities and ideas shape what states want in the first place; interests are socially constructed, not fixed by material structure. Anarchy is what states make of it.
Constructivism still works mainly at the level of states, but its real focus is the ideas, norms and identities that shape them, and it studies how norms cascade across the system rather than treating states as fixed units.
Constructivism rejects the idea that anarchy has a single meaning. Wendt argues anarchy is what states make of it: the same structure can produce Hobbesian, Lockean or Kantian cultures depending on what states believe.
Whether states cooperate depends on the culture of anarchy that predominates. Western Europe shifted from Hobbesian enemies to largely Kantian friends, so durable cooperation is possible but ideationally contingent.
Constructivists study how norms spread and become taken for granted, such as the norm against chemical weapons. Norms and rules matter, but they work through shared belief rather than as material institutional constraints.
Constructivism rejects a fixed, pessimistic human nature. The same structural condition can produce different behaviours depending on what states believe about themselves and others.
Constructivism holds that what states want flows from who they think they are. Germany's post-1945 anti-militarist identity, and the 2022 Zeitenwende rearmament, show identity-driven behaviour realism cannot explain.