International politics unfolds between the pursuit of principles and the demands of security. Realism examines this tension by placing states, national interests and the distribution of power at the centre of its analysis. Its different schools offer competing explanations of why governments cooperate, compete and go to war.
1. Realism and Realpolitik: An Essential Distinction
Understanding this tradition requires distinguishing it from Realpolitik. The term was coined by the German writer August Ludwig von Rochau in 1853, although attention to political necessity is much older. Realpolitik generally describes a practical approach attentive to existing conditions and power relations. Realism encompasses a broader family of theories about international politics, with disagreements over both explanation and political judgement.
2. The Classical Roots: Thucydides, Machiavelli and Hobbes
The tradition’s intellectual ancestry is often traced to Thucydides and his account of the Peloponnesian War. In the Melian Dialogue, set in 416 BC, Athenian representatives confront the inhabitants of Melos with the consequences of unequal power: “the strong do what they can and the weak suffer what they must.” These are words attributed to the Athenians within the narrative. Treating them as Thucydides’ personal endorsement of domination overlooks the moral tensions of his history.
Centuries later, Machiavelli examined how rulers acquire and preserve authority. The Prince explored the conflict between conventional virtues and political survival. Yet its argument is more qualified than the familiar celebration of ruthlessness suggests: a ruler who relies on fear must also avoid becoming hated. Political judgement involves anticipating the consequences of coercion.[4]
Thomas Hobbes supplied another influential foundation in Leviathan (1651). Without a common authority capable of enforcing agreements, insecurity can persist even when individuals desire peace. His state of war includes the continuing expectation of violence, rather than uninterrupted fighting. Hobbes favoured monarchy, but his sovereign could also take the form of an assembly. His central concern was the establishment of an effective, undivided authority.
3. The Emergence of Modern Classical Realism
Modern realism became a distinct academic force during the upheavals surrounding the Second World War. In The Twenty Years’ Crisis (1939), E. H. Carr challenged the confidence placed in international principles detached from the distribution of power. Significantly, his book also examined the limitations of realism itself. The relationship between power and morality remained a problem to investigate. The catastrophe of war increased realism’s influence without establishing the scientific truth of every realist proposition.
Hans Morgenthau subsequently gave classical realism one of its most influential formulations in Politics Among Nations, first published in 1948. Its second edition, in 1954, introduced his famous six principles. These connected politics to human nature, interpreted interest through power, recognised the historically changing content of interests, stressed prudence in moral judgement, rejected the identification of national aspirations with universal morality, and defended the autonomy of political analysis. Morgenthau nevertheless retained an ethical concern with responsibility: leaders had to consider the foreseeable consequences of their decisions.
4. Neorealism: The International System Takes Centre Stage
Kenneth Waltz shifted the explanation towards the international system in Theory of International Politics (1979). His structural realism, commonly called neorealism, centred on anarchy: the absence of an overarching authority above sovereign states. Survival was the minimum objective states had to secure before pursuing other goals. In this environment, governments faced pressures to provide for their security through domestic capabilities and external alliances. This principle of self-help therefore accommodated cooperation between states.
For Waltz, the distribution of capabilities also shaped international outcomes. A bipolar system has two predominant powers; a multipolar system has several; unipolarity denotes the predominance of one. He argued that bipolarity reduced certain uncertainties surrounding threats and alliance commitments. This was a comparative argument about systemic stability, rather than a guarantee of peace or an assertion that a bipolar world would be free of regional wars.
5. The Security Dilemma and the Possibility of Cooperation
One of the tradition’s central mechanisms is the security dilemma. Measures intended to protect one state can appear threatening to another, encouraging reciprocal military preparations. However, insecurity does not increase mechanically whenever a government strengthens its defences.
Robert Jervis showed in his 1978 study that cooperation becomes more feasible under certain conditions, including when defensive postures can be distinguished from offensive preparations. Mutual gains remain possible; international security cannot always be reduced to a zero-sum contest.
6. Defensive and Offensive Realism
Disagreement over how states achieve security helped distinguish defensive and offensive realism. Defensive realists, associated with Waltz and Jervis, emphasise the dangers of excessive expansion: attempts at domination can provoke counterbalancing and leave the aggressor less secure.
Offensive realism, most prominently developed by John Mearsheimer in The Tragedy of Great Power Politics (2001), assigns stronger incentives to accumulating relative power. Since governments cannot be certain of others’ future intentions, great powers seek opportunities to improve their position and, where feasible, achieve regional hegemony. Survival remains the ultimate objective; expanding power is the strategy through which states attempt to secure it. The disagreement concerns how much power provides sufficient security.
7. Neoclassical Realism: Bringing Domestic Politics Back In
Neoclassical realism addresses a further question: how do international pressures become particular foreign policies? Gideon Rose introduced the label in a 1998 article describing research that connected relative material power with domestic conditions.
Leaders’ perceptions, political institutions and the state’s capacity to mobilise resources mediate the effects of the international environment. Governments facing similar external pressures may consequently adopt different strategies. This approach gives domestic politics a larger explanatory role while retaining the realist emphasis on power.
8. Criticisms, Limits and Enduring Relevance
Realism’s critics challenge both its assumptions and its explanatory reach. Robert Keohane’s institutional approach explains how international arrangements can sustain cooperation among governments pursuing their own interests. Alexander Wendt’s constructivism questions whether anarchy necessarily produces a single competitive logic, emphasising how interaction shapes identities and interests. These debates concern the influence of institutions, ideas and relationships alongside material capabilities.
Realism remains valuable when it makes political analysis more attentive to constraints, uncertainty and unintended consequences. Its usefulness depends equally on recognising its limits. Explaining the pressures behind a government’s conduct leaves open the questions of legality, responsibility and moral judgement. Power helps explain what states can do; it cannot, by itself, settle what they should do.
