1.4 Defensive realism

Defensive realism overview

Defensive realism explains how states behave in an anarchic international system where no higher authority exists to protect them. Rather than seeking maximum power, states focus on survival and security by maintaining a balance of power. This distinction matters because it leads to very different predictions about war, alliances, and cooperation than its counterpart, offensive realism.

The theory is most closely associated with Kenneth Waltz's structural realism (from Theory of International Politics, 1979) and was further developed by scholars like Stephen Van Evera and Charles Glaser. It sits within the broader realist tradition but offers a more restrained view of what states actually want.

Assumptions of defensive realism

Defensive realism rests on several core assumptions about how the international system works:

• Anarchy defines the international system. There is no world government or central authority to enforce rules, settle disputes, or guarantee any state's safety.
• States are the primary actors and are treated as unitary, rational decision-makers. This means the theory focuses on what states do as coherent units rather than on internal politics or individual leaders.
• Survival is the primary goal. States care most about ensuring their continued existence and security, not about accumulating power for its own sake.
• Uncertainty about intentions is constant. Because states can never fully know whether other states are peaceful or aggressive, they tend to focus on relative gains and on maintaining a favorable balance of power.

Defensive realism vs. offensive realism

These two branches of structural realism share the same starting point (anarchy, rational states, the importance of power) but reach different conclusions about what states should do.

Theoretical foundations

Defensive realism builds on the core logic of structural realism, which holds that the structure of the international system (not the internal characteristics of states) drives state behavior. It draws heavily on two related concepts: the security dilemma and balance of power theory.

Role of anarchy in defensive realism

Anarchy doesn't mean chaos. It means there's no authority above states to call the shots. This creates a self-help system where every state must look after its own security using its own capabilities.

This has a few important consequences:

• States can't trust that agreements will be enforced, so they remain vigilant about potential threats.
• Relative power matters constantly, because a state that falls behind may not be able to defend itself.
• Anarchy doesn't guarantee conflict, but it does create persistent incentives for states to prioritize security over other goals.

Implications of uncertainty

States can never be fully certain whether another state's intentions are benign or hostile. This uncertainty shapes behavior in concrete ways:

• States tend to plan for worst-case scenarios. Even if a neighbor is probably peaceful, the cost of being wrong is too high to ignore.
• Shifts in the distribution of power create anxiety. A rising state might be peaceful today but threatening tomorrow, so other states hedge against that possibility.
• Defensive measures like arms buildups, even when genuinely intended for protection, can look threatening to others. This is where the security dilemma kicks in (more on that below).

Importance of relative power

In an anarchic system, what matters is not how powerful you are in absolute terms but how powerful you are compared to potential rivals.

A state might turn down an economic deal that benefits both sides if the other state gains disproportionately. For example, if a trade agreement gives State A $5 billion in growth but gives its rival State B $15 billion, State A may reject it. The absolute gain is positive, but the relative gain favors a potential competitor. This focus on relative gains over absolute gains is a defining feature of realist thought and a key reason defensive realists see limits to cooperation.

Security-seeking behavior

If survival is the goal, how do states actually pursue it? Defensive realism identifies several strategies, all oriented around maintaining a favorable balance of power without provoking unnecessary hostility.

Strategies for survival

States have three main options for managing threats:

1. Internal balancing means building up your own capabilities. This includes military spending, weapons development, and economic growth that supports a stronger defense posture. A state investing heavily in its own military rather than relying on allies is internally balancing.

2. External balancing means forming alliances with other states to counterbalance a common threat. NATO during the Cold War is the classic example: Western European states allied with the United States to counter Soviet power.

3. Buck-passing means trying to get someone else to bear the cost of confronting a rising threat. Instead of balancing directly, a state encourages others to do the heavy lifting. France and Britain's reluctance to confront Nazi Germany in the late 1930s, each hoping the other (or the Soviet Union) would check Hitler's expansion, is often cited as an example of buck-passing.

Balancing vs. bandwagoning

When a powerful or threatening state emerges, other states face a choice:

• Balancing: joining together to oppose the threatening power. Defensive realism predicts this is the more common response, because it preserves autonomy and prevents any single state from dominating.
• Bandwagoning: siding with the threatening or dominant power, essentially hoping to gain protection or rewards by aligning with the stronger side. Eastern European states joining the Soviet-led Warsaw Pact is a frequently cited example.

Defensive realism generally expects balancing to prevail. Bandwagoning is risky because it makes a state dependent on the dominant power and vulnerable to its demands. Stephen Walt's balance of threat theory refines this further, arguing that states balance against the most threatening power (not just the most powerful one), taking into account geographic proximity, offensive capabilities, and perceived aggressive intentions.

Pursuit of moderate power

This is one of defensive realism's most distinctive claims: states should seek enough power to be secure, but not so much that they alarm everyone else.

Pursuing excessive power triggers balancing coalitions. Other states, fearing domination, will ally against you, leaving you less secure than before. Think of Napoleonic France or Wilhelmine Germany: both pursued aggressive expansion and ended up facing broad coalitions that ultimately defeated them.

The practical implication is that status-quo behavior is usually the smartest strategy. States should avoid actions that look aggressive or revisionist, because the systemic punishment (other states ganging up on you) outweighs the short-term gains.

Cooperation under defensive realism

Unlike some versions of realism that see cooperation as nearly impossible, defensive realism allows for meaningful cooperation among states. But it also identifies clear constraints on how deep or lasting that cooperation can be.

Possibility of cooperation

States can and do cooperate, especially when facing shared threats:

• Collective defense organizations like NATO pool military resources against a common adversary, reducing the individual cost of security for each member.
• States may cooperate to manage regional security problems, such as arms control agreements that reduce the risk of accidental conflict.
• Cooperation can also take the form of establishing norms and institutions that make state behavior more predictable, reducing some of the uncertainty that anarchy creates.

Limits to cooperation

Cooperation in an anarchic system always runs into structural obstacles:

• Fear of cheating: without enforcement, states worry that partners will defect from agreements when it suits them. An arms control treaty is only as good as each side's willingness to comply.
• Relative gains concerns: even mutually beneficial cooperation can be undermined if one side gains more than the other, shifting the balance of power.
• Autonomy costs: relying on allies for security creates dependence. If an ally's interests shift, a state that has neglected its own capabilities is left exposed.

For these reasons, cooperation tends to be issue-specific and shorter-term rather than deeply institutionalized. States cooperate when it serves their security interests and pull back when it doesn't.

Impact of the security dilemma

The security dilemma is one of the most important concepts in defensive realism. It describes a tragic dynamic: when one state takes steps to increase its own security (building up its military, developing new weapons), other states perceive those steps as threatening and respond with their own buildups. The result is an arms race that leaves everyone less secure, even though no one intended aggression.

This dynamic can poison cooperation. Even states with genuinely defensive intentions can end up locked in spirals of mistrust and competition. The Cold War arms race between the U.S. and the Soviet Union is a textbook case.

Defensive realists argue that the security dilemma can be mitigated through:

• Signaling benign intentions, such as adopting transparently defensive military postures
• Confidence-building measures, like arms inspections, hotlines between governments, or mutual troop withdrawals from border areas
• Distinguishing between offensive and defensive weapons (though this distinction is often blurry in practice)

Critiques of defensive realism

Defensive realism has shaped how scholars and policymakers think about international security, but it faces several significant criticisms.

Challenges to key assumptions

• Overemphasis on systemic structure: critics argue that defensive realism gives too much weight to anarchy and not enough to domestic politics, regime type, leadership psychology, or non-state actors. A democratic peace theorist, for instance, would point out that democracies rarely fight each other, something structural realism struggles to explain.
• The unitary rational actor assumption is a simplification. In reality, foreign policy is shaped by bureaucratic politics, public opinion, interest groups, and individual leaders' personalities and misperceptions. Graham Allison's work on the Cuban Missile Crisis showed how bureaucratic processes, not just rational calculation, drove decision-making.
• Survival as the sole primary goal may be too narrow. States sometimes pursue ideological objectives, national prestige, or domestic political goals that don't reduce neatly to security-seeking. The U.S. invasion of Iraq in 2003 is difficult to explain purely through a defensive realist lens.

Empirical limitations

• World War I is a tough case for defensive realism. The theory predicts that states should avoid aggressive expansion, yet the major European powers stumbled into a catastrophic war, arguably through the very security dilemma dynamics the theory describes but failed to prevent.
• The end of the Cold War is another puzzle. Defensive realism doesn't easily explain why the Soviet Union chose to peacefully dissolve rather than fight to maintain its position in the balance of power.
• Some states have pursued revisionist or expansionist policies that don't fit the theory's prediction of moderate, status-quo behavior. If the system incentivizes restraint, why do some states still overexpand?

Comparison to alternative theories

Defensive realism is one lens among several. Understanding where it differs from alternatives helps clarify what it does and doesn't explain well.

• Offensive realism (Mearsheimer) shares the structural framework but reaches the opposite policy conclusion: states should maximize power whenever possible because the system is too dangerous to settle for "enough."
• Liberal IR theory emphasizes factors defensive realism largely ignores: democratic governance, international institutions, and economic interdependence as forces that can promote peace and cooperation beyond what anarchy alone would predict.
• Constructivism challenges defensive realism's materialism entirely. Constructivists like Alexander Wendt argue that "anarchy is what states make of it," meaning that shared ideas, norms, and identities shape whether anarchy produces conflict or cooperation. The structure of the system matters less than how states interpret that structure.