Series: Realism Foundations: Classical vs. Structural Realism
The Intellectual War to Define a Ruling Theory of Global Power Dynamics
In the world of international relations, few debates are as central as the divide between classical realism and structural realism. Both schools fall under the broader realist tradition, which views international politics as a contest for power in an anarchic world. Yet, they offer distinct explanations for why states pursue power and why conflicts emerge. Classical realism finds the source in human nature and political ambition, while structural realism argues that the international system itself compels states to compete. Understanding this divide is key to grasping the foundations of realism and its enduring relevance in global affairs.
Classical Realism: Human Nature and the Drive for Dominance
Classical realism, with roots in thinkers like Thucydides, Machiavelli, and Hobbes, sees the struggle for power as a consequence of human nature. In this view, states act aggressively because their leaders are driven by ambition, fear, and the desire for prestige. Hans Morgenthau, one of the most influential classical realists, argued that politics, both domestic and international, is governed by objective laws rooted in human behavior. In Politics Among Nations (1948), Morgenthau asserted that states pursue power because leaders, as humans, are compelled by an insatiable will to dominate.
Classical realism places a strong emphasis on the role of leadership, ideology, and historical experience. Wars, alliances, and rivalries are often shaped by individual decisions and the pursuit of glory or security. This view helps explain conflicts that seem irrational from a purely strategic perspective. For example, Thucydides’ account of the Peloponnesian War highlights how fear, pride, and honor—not just strategic calculation—drove Athens and Sparta into a devastating conflict.
Another hallmark of classical realism is its pragmatic approach to morality. Realists of this school argue that morality has little place in international politics, where survival is paramount. Prudence—the careful calculation of power and interest—is the highest virtue. For Morgenthau, successful statesmanship requires aligning moral aspirations with the realities of power, recognizing that moral principles cannot be upheld without strength.
Structural Realism: The System Shapes the State
Structural realism, also known as neorealism, shifts the focus from human nature to the structure of the international system. Developed by Kenneth Waltz in Theory of International Politics (1979), this variant of realism argues that the anarchic nature of the international system compels states to seek security through power. Waltz contended that states behave similarly not because they share the same ambitions but because they operate within the same structural constraints—namely, a world without a central authority.
In a self-help system, where no state can rely on others for protection, survival becomes the paramount goal. States are forced to accumulate power because power is the currency of security. Structural realists argue that this competitive behavior is driven not by human nature or ideology but by the logic of the system itself. As a result, even states with peaceful intentions are pushed to arm themselves, leading to what is known as the security dilemma: measures taken by one state to increase its security often make other states feel less secure, triggering arms races and conflicts.
Waltz also introduced the concept of polarity—the distribution of power across the international system—as a key determinant of stability. He argued that bipolar systems, such as the U.S.-Soviet rivalry during the Cold War, are more stable than multipolar systems because they reduce uncertainty and the likelihood of miscalculation. In contrast, multipolar systems, with their shifting alliances and multiple great powers, are more prone to instability and conflict.
Defensive vs. Offensive Realism: A Split Within Structural Realism
Although all structural realists agree that the anarchic international system drives state behavior, they differ on how much power states should pursue. This divide has produced two major strands: defensive realism and offensive realism.
Defensive realists, led by Kenneth Waltz, argue that states seek only enough power to ensure their survival. Accumulating excessive power, Waltz warned, is self-defeating because it provokes balancing behavior from other states. In a balanced system, states recognize that attempts at hegemony will ultimately lead to counter-coalitions and prolonged conflicts. The Cold War’s balance of power, where the U.S. and the Soviet Union avoided direct war through mutual deterrence, is often cited as an example of defensive realism in practice.
Offensive realists, such as John Mearsheimer, reject this notion, contending that states should pursue as much power as possible. According to Mearsheimer, the inherent uncertainty of international politics means that states can never be sure of each other’s intentions. As a result, the best path to security is to become the most powerful actor in the system. Offensive realists argue that regional hegemony—domination within a specific geographical area—is the ultimate goal. Mearsheimer’s predictions regarding U.S.-China relations are a prime example of this logic: he argues that China’s rise will inevitably lead to conflict with the United States, as both powers strive for dominance in the Asia-Pacific region.
Classical vs. Structural Realism: Key Differences
The most fundamental difference between these two schools of realism lies in their explanation of the causes of conflict. Classical realists see conflict as a consequence of human nature—leaders act aggressively because they are driven by fear, pride, and ambition. In contrast, structural realists argue that it is the anarchic structure of the international system, not human nature, that compels states to compete.
Additionally, the two schools differ in their conception of power. For classical realists, power is both a means and an end—states seek power not only for security but also for prestige and influence. Structural realists, however, see power primarily as a means to security. States pursue power not because they desire dominance for its own sake, but because the system leaves them no choice.
Another important contrast is their treatment of morality and decision-making. Classical realists consider the moral dimensions of power politics, though they prioritize pragmatism over idealism. They emphasize the role of statesmen, leadership, and individual judgment in shaping world events. Structural realists, by contrast, see leaders as largely interchangeable—the system, not the individual, dictates outcomes.
Realism in Action: Applying the Theories to Global Conflicts
The divergence between classical and structural realism becomes evident when applied to historical and contemporary conflicts.
During the Cold War, classical realists might emphasize the role of ideology and leadership—the personalities and ambitions of leaders such as Stalin, Truman, and Reagan in escalating or easing tensions. In contrast, structural realists argue that the Cold War was an inevitable consequence of bipolarity. With only two superpowers in a self-help system, competition for power was unavoidable regardless of leadership or ideology.
In the ongoing U.S.-China rivalry, offensive realists such as John Mearsheimer argue that China’s rise will inevitably lead to conflict, as a rising power seeks to challenge the existing hegemon. Defensive realists, however, suggest that careful management of the balance of power, through diplomacy and deterrence, can prevent escalation. A classical realist perspective might highlight the role of nationalism, historical memory, and leadership decisions—factors that could either escalate or moderate the rivalry depending on how they are managed.
The Relevance of Realism Today
Both classical and structural realism remain indispensable for understanding contemporary global politics. From the resurgence of great power competition to regional conflicts and shifting alliances, realism offers a sober assessment of international behavior. Classical realism reminds us that ambition, pride, and fear continue to drive state actions, while structural realism highlights how the international system shapes those behaviors regardless of intentions or morality.
In the face of emerging challenges—rising powers, economic decoupling, technological competition, and nuclear deterrence—realism offers not only a framework for analysis but also a guide for strategy. It warns against utopianism in foreign policy, emphasizing that power and security, not ideals or aspirations, remain the primary currencies of international politics.
For those who study global affairs through a realist lens, the debate between classical and structural realism is more than theoretical—it is foundational. Understanding both perspectives is essential for anyone seeking to navigate the complexities of an anarchic world where power remains the ultimate arbiter of security and survival.
This article is part of Global Realist's "Realism Foundations" series. In the next installment, we will explore Offensive vs. Defensive Realism, breaking down the internal debates within structural realism and their implications for contemporary geopolitics.