1.2 Structural realism (neorealism)

Key assumptions of structural realism

Structural realism (neorealism) is a theory that explains state behavior by looking at the international system itself rather than what's happening inside individual states. Kenneth Waltz developed it in his 1979 book Theory of International Politics as a response to classical realism, which rooted conflict in human nature and the internal characteristics of states. Neorealism makes a different argument: the structure of the international system, defined by anarchy and the distribution of power among states, is what primarily drives how states act and what outcomes we see in world politics.

Anarchy in the international system

Absence of central authority

Anarchy in IR doesn't mean chaos or disorder. It means there is no governing authority above sovereign states. In domestic politics, a government maintains order, enforces laws, and punishes rule-breakers. The international system has no equivalent. There's no world government that can force states to behave a certain way or protect them when they're threatened.

Because no higher authority exists, states must rely on self-help to ensure their survival and pursue their interests. This is the foundational condition that shapes everything else in neorealist theory.

Self-help system for states

In a self-help system, each state is ultimately responsible for its own security. You can't count on another state to come to your rescue, because today's ally could be tomorrow's rival. This creates a competitive environment where states prioritize building their own power and capabilities.

• States invest in military strength as insurance against threats
• Cooperation happens, but it's always constrained by the worry that partners might gain a strategic advantage
• Even peaceful states get pulled into competitive behavior because the system's structure demands it

The key insight here is that it's not necessarily ambition driving conflict. It's the structure of the system itself.

Structure as the key determinant

Distribution of power among states

For Waltz, the most important feature of international structure (beyond anarchy, which is constant) is how power is distributed among states. Power is typically measured through material capabilities: military strength, economic output, population, natural resources, and technological capacity.

The relative power of states determines what options they have. A great power can project force globally and shape international rules. A small state has far fewer options and must adapt to the system that larger states create.

Polarity and its implications

Polarity refers to the number of great powers in the system at any given time:

• Unipolar: One dominant great power (e.g., the United States after 1991)
• Bipolar: Two dominant great powers (e.g., the U.S. and Soviet Union during the Cold War)
• Multipolar: Three or more great powers (e.g., Europe before World War I)

Waltz argued that bipolar systems tend to be more stable than multipolar ones. His reasoning: with only two major powers, each side can focus on the other, miscalculation is less likely, and there are fewer shifting alliances to create uncertainty. In multipolar systems, the web of relationships is more complex, making miscalculation and accidental escalation more probable.

State behavior and motivation

Survival as the primary goal

Neorealism treats survival as the baseline goal of every state. Before a state can pursue economic growth, spread its ideology, or promote human rights, it first needs to exist. In an anarchic system with no one to call for help, protecting sovereignty and territorial integrity comes before everything else.

This survival imperative shapes concrete policy choices: states build militaries, form alliances, and make strategic calculations all with an eye toward ensuring they aren't conquered or coerced.

Relative gains vs. absolute gains

This is a concept that trips students up, so it's worth being precise. Absolute gains means asking, "Am I better off than before?" Relative gains means asking, "Am I better off compared to the other state?"

Neorealists argue that states care deeply about relative gains. Even if a trade deal makes both countries wealthier, a state will hesitate if the other side gains more, because that extra wealth could eventually be converted into military power. This concern about relative gains is a major reason neorealists are skeptical about deep international cooperation. States worry that helping others might ultimately undermine their own security position.

Balance of power theory

Internal balancing through military buildup

When a state perceives a growing threat, one response is internal balancing: strengthening its own capabilities from within.

• Expanding armed forces or increasing defense spending
• Developing new weapons systems or military technologies
• Investing in economic capacity that supports military power

The logic is straightforward: if you're strong enough, potential aggressors will think twice before challenging you.

External balancing through alliances

The other response is external balancing: forming alliances to pool resources and capabilities against a common threat.

• NATO during the Cold War is the classic example, where Western states aligned against the Soviet Union
• Alliances allow smaller states to counter a larger threat they couldn't handle alone
• Alliance commitments also serve as signals to adversaries, raising the perceived cost of aggression

States often use both strategies simultaneously. During the Cold War, the U.S. maintained massive military forces (internal balancing) and built a network of alliances across Europe and Asia (external balancing).

Security dilemma

Uncertainty about intentions of others

The security dilemma is one of the most important concepts in neorealism. It describes a situation where one state's efforts to increase its own security make other states feel less secure, even when no one intends aggression.

Here's how it works: State A builds up its military purely for defense. State B can't be sure those forces are defensive. State B responds by building up its own military. State A sees State B arming and feels threatened. Both sides end up less secure than when they started, despite neither wanting conflict.

The root cause is uncertainty about intentions. In an anarchic system, you can observe another state's capabilities but you can never be fully certain about its intentions.

Spiral model vs. deterrence model

These two models offer competing predictions about how states should respond to the security dilemma:

• Spiral model: When states respond to perceived threats by arming, it triggers a cycle of escalation. Each side's defensive moves look offensive to the other, and tensions spiral upward. The arms race between Britain and Germany before World War I is a frequently cited example. The prescription here is restraint and reassurance.
• Deterrence model: States can maintain stability by clearly demonstrating military strength and the resolve to use it. If a potential aggressor believes retaliation is certain and severe, it won't attack. Cold War nuclear deterrence between the U.S. and USSR illustrates this logic.

The challenge for policymakers is figuring out which model applies in a given situation. If you show restraint when deterrence is needed, you invite aggression. If you escalate when the spiral model applies, you make war more likely.

Offensive vs. defensive realism

Maximizing power vs. maintaining security

Neorealism splits into two major camps that disagree about how much power states should seek:

• Offensive realism (associated with John Mearsheimer) argues that states can never be sure how much power is "enough" for survival. The rational response is to maximize power whenever the opportunity arises, ultimately seeking regional hegemony. States that settle for less leave themselves vulnerable.
• Defensive realism (associated with Waltz and others like Stephen Van Evera) argues that the system usually punishes overly aggressive states. Expansion tends to provoke balancing coalitions that leave the aggressor worse off. States are better served by maintaining a moderate level of power and avoiding unnecessary provocation.

Implications for state behavior

These two branches generate different predictions about how states will act:

• Offensive realism predicts that great powers will actively seek to expand influence, pursue military superiority, and exploit power vacuums. Mearsheimer uses this framework to explain why a rising China is likely to challenge U.S. dominance in Asia.
• Defensive realism predicts that states will generally prefer the status quo and avoid actions that trigger counterbalancing. Aggressive expansion, like Napoleon's or Hitler's, is seen as a strategic error rather than rational behavior.

Which branch better explains reality is an ongoing debate in the field. The answer often depends on factors like geography, the offense-defense balance in military technology, and how clearly states can signal their intentions.

Critiques of structural realism

Neglect of domestic factors

One of the most common criticisms is that neorealism treats states as interchangeable "black boxes." It doesn't matter whether a state is a democracy or a dictatorship, wealthy or poor, ideologically driven or pragmatic. The system's structure supposedly determines behavior regardless.

Critics point out that domestic factors clearly matter. Democratic peace theory, for instance, argues that democracies rarely go to war with each other, something neorealism's systemic focus can't explain. Political institutions, public opinion, ideology, and leadership all shape how states respond to international pressures, and neorealism has little to say about any of them.

Challenges to the rational actor model

Neorealism assumes states behave as unitary, rational actors that weigh costs and benefits and choose the option that best serves their survival. Critics raise several problems with this:

• Individual leaders don't always act rationally. Cognitive biases, misperceptions, and emotional reactions influence decision-making.
• Bureaucratic politics within governments can produce policies that no single rational actor would choose. Different agencies compete, and outcomes reflect internal bargaining rather than strategic calculation.
• Some state behavior, like ideologically motivated wars that clearly damage the state's interests, is hard to square with the rational actor assumption.

These critiques don't necessarily invalidate neorealism, but they highlight its limits as an explanatory framework.

Empirical applications and case studies

Cold War era international politics

The Cold War is neorealism's strongest case study. The bipolar structure of the system, with the U.S. and Soviet Union as the two dominant powers, maps neatly onto the theory's predictions:

• Both superpowers engaged in extensive internal and external balancing (massive arms buildups, rival alliance systems in NATO and the Warsaw Pact)
• The security dilemma played out through the nuclear arms race, where each side's arsenal made the other feel less secure
• Deterrence theory, particularly mutually assured destruction (MAD), helped explain why the two superpowers avoided direct military conflict despite intense rivalry
• The bipolar system remained relatively stable for over four decades, consistent with Waltz's prediction about bipolar stability

Post-Cold War world order

The Soviet Union's collapse in 1991 created significant challenges for neorealist theory. If the system's structure determines behavior, neorealism should have predicted the Cold War's end, but it largely didn't. Several ongoing debates have emerged:

• The shift to unipolarity under U.S. dominance raised questions about whether other states would balance against American power, as the theory predicts. Balancing has been slower and weaker than many neorealists expected.
• The growing importance of non-state actors (terrorist organizations, multinational corporations, international NGOs) challenges neorealism's state-centric framework.
• Issues like globalization, climate change, and cyber threats don't fit neatly into a theory built around military power and territorial security.

Neorealists respond that the theory still captures the most important dynamics in great power politics, pointing to U.S.-China competition and Russia's reassertion of regional influence as evidence that power distribution continues to shape international outcomes.