Definition of balance of power
Balance of power theory explains how states try to prevent any single nation from becoming dominant enough to threaten everyone else. In an anarchic international system with no world government to keep order, states pursue strategies to keep power distributed broadly enough that no one actor can impose its will. This theory sits at the heart of the realist tradition and has shaped how scholars and policymakers think about war, alliances, and stability for centuries.
The core logic is straightforward: when one state grows too powerful, other states respond by building up their own capabilities or forming alliances to counterbalance it. The theory assumes states act as rational, security-seeking units that pay close attention to shifts in relative power.
Meaning in international relations
In IR, "balance of power" describes a system where no single state or coalition can dominate the rest. States are in constant competition for power and influence, and the resulting equilibrium is what preserves each state's security and autonomy.
Realists treat the balance of power as more than just a description of how things are. It also functions as a prescriptive principle: states should act to prevent hegemony because a system in rough equilibrium is less likely to produce major wars. When the balance holds, aggression becomes too costly for any single state to attempt.
Historical origins
The concept has deep roots stretching back to ancient Greek political thought. Thucydides' account of the Peloponnesian War, where Greek city-states aligned against growing Athenian power, is often read as an early balance-of-power narrative. His famous line about Sparta's fear of rising Athenian power captures the core balancing impulse.
The modern version of the theory took shape in Europe during the 16th and 17th centuries, as states maneuvered to prevent any single power from dominating the continent. The Habsburg Empire and later France under Louis XIV were the primary threats that drove balancing behavior.
The Peace of Westphalia (1648) is a key turning point. By establishing the principles of state sovereignty and non-interference, Westphalia created the framework of independent, legally equal states that balance of power theory takes as its starting point.
Types of balance of power
States don't all balance in the same way. The strategy a state chooses depends on its capabilities, geographic position, threat perception, and the structure of the international system at the time.
Hard vs. soft balancing
Hard balancing involves direct military measures: arms buildups, formal alliance commitments, and the deployment of forces to counter a specific threat. NATO during the Cold War is the classic example, with Western states pooling military resources to deter Soviet expansion.
Soft balancing uses economic, diplomatic, and institutional tools to constrain a powerful state without overt military confrontation. States might coordinate votes in international organizations, form economic partnerships, or use diplomatic signaling to limit a rival's freedom of action. T.V. Paul's work on soft balancing highlights how states used this approach against the U.S. after the 2003 Iraq invasion, with France, Germany, and Russia coordinating opposition through the UN Security Council. States tend to choose soft balancing when the threat isn't severe enough to justify military mobilization, or when they lack the capability for hard balancing.
Offshore balancing
Offshore balancing is a strategy where a geographically distant great power maintains regional equilibrium by supporting local allies rather than deploying its own forces directly. The offshore balancer intervenes militarily only as a last resort, when local states can't contain a rising regional hegemon on their own.
The United States has periodically pursued this approach, particularly in the Middle East and East Asia. John Mearsheimer is one of the strongest advocates for this strategy, arguing that it conserves resources and avoids the political and human costs of sustained military presence abroad.
Buck-passing
Buck-passing occurs when a state tries to shift the burden of balancing onto someone else. Instead of confronting a rising threat directly, the buck-passer hopes that other states in the system will bear the costs and risks.
Britain's response to Nazi Germany in the 1930s is a frequently cited example. Britain hoped that France and the Soviet Union would contain German expansion, delaying its own full commitment. The danger of buck-passing is obvious: if every state tries to pass the buck, no one balances effectively, and the threatening power grows unchecked. This can lead to catastrophic miscalculation, as it arguably did in the late 1930s.
Mechanisms of balance of power
States use both internal and external mechanisms to maintain or restore equilibrium. These aren't mutually exclusive; most states pursue some combination of both.
Alliances and coalitions
Alliances are the primary external balancing mechanism. States pool their resources and commit to mutual defense against a common threat. These can range from formal treaty obligations (NATO's Article 5, which treats an attack on one member as an attack on all) to informal alignments based on shared interests.
Alliance formation involves real tradeoffs. States gain security but sacrifice some autonomy, and they face collective action problems: every member has an incentive to free-ride on others' contributions. Glenn Snyder's "alliance security dilemma" captures this tension well. States worry about two opposite risks: abandonment (your ally won't help when you need it) and entrapment (your ally drags you into a conflict you'd rather avoid). Managing these tensions is a constant challenge.
Internal balancing through military buildup
Internal balancing means increasing your own power rather than relying on allies. This includes expanding military forces, investing in new weapons systems, and pursuing economic development to fund greater capabilities.
China's ongoing military modernization is a prominent contemporary example. Since the 1990s, China has dramatically expanded its naval capabilities, developed advanced missile systems, and increased its defense spending (estimated at over $290 billion annually by some measures). Internal balancing gives a state more control over its own security, but it's expensive and time-consuming, and it can trigger arms races as rivals respond in kind.
External balancing through diplomacy
Diplomacy serves as a balancing tool when states use political and economic leverage to build coalitions, isolate adversaries, or resolve disputes before they escalate. The U.S.-led effort to build an international coalition imposing sanctions on Iran's nuclear program illustrates this approach.
Effective diplomatic balancing requires credible commitments, skilled negotiation, and the strategic use of both incentives and penalties. It also depends on the willingness of other states to cooperate, which brings us back to the collective action problems that make balancing difficult in practice.
Conditions for balance of power
Balance of power theory rests on several key assumptions about how the international system works. If these conditions don't hold, the theory's predictions weaken.
Anarchy in the international system
The theory assumes there is no overarching authority above states. In this condition of anarchy, no world government exists to enforce rules, punish aggressors, or guarantee anyone's safety. States must rely on self-help to survive. This creates the competitive dynamic that drives balancing behavior in the first place. Kenneth Waltz made anarchy the foundational structural condition in his neorealist theory, arguing that it constrains state behavior regardless of what individual leaders want.
Rational state behavior
States are assumed to be rational actors that weigh costs and benefits before acting. They assess threats, calculate the distribution of power, and choose strategies that maximize their security. Without this assumption, the theory can't predict that states will reliably balance against rising powers.
If states act irrationally or are driven by ideology or domestic politics rather than strategic calculation, balancing may not occur as expected. This is one reason why the theory sometimes struggles to explain cases like Napoleonic France or Nazi Germany, where ideological ambition overrode cautious strategic calculation.
Relative gains concerns
Realists argue that states care more about relative gains (how much power they have compared to rivals) than absolute gains (how much they benefit overall). Even a mutually beneficial trade deal can be threatening if it benefits your rival more than it benefits you, because that shifts the balance of power.
This focus on relative gains makes cooperation difficult and reinforces the competitive logic of balancing. States are reluctant to allow rivals to gain disproportionate advantages, even when cooperation might make everyone better off in absolute terms. Joseph Grieco's work on this point is a key reference for understanding why realists are skeptical of international cooperation.
Challenges to balance of power
Several competing theories and real-world developments challenge the predictions and assumptions of balance of power theory.
Hegemonic stability theory
Hegemonic stability theory argues that a dominant power can actually promote stability rather than provoke balancing. A hegemon may provide public goods like open trade routes, security guarantees, and international institutions that benefit the whole system.
The Pax Britannica (19th century) and Pax Americana (post-1945) are the standard examples. In both cases, a preponderant power underwrote international order, and other states largely accepted rather than challenged that dominance. This directly contradicts the balance of power prediction that states will inevitably resist hegemony.
Bandwagoning behavior
Bandwagoning is the opposite of balancing: instead of opposing the strongest power, states align with it. States may bandwagon when they judge the costs of resistance to be too high, or when they hope to share in the dominant power's success.
Stephen Walt's balance of threat theory refines this picture. Walt argues that states don't simply balance against power but against threat, which includes a state's aggregate power, geographic proximity, offensive capabilities, and perceived aggressive intentions. This helps explain why bandwagoning is more common among weak states facing an immediate threat, while balancing is more typical among great powers. Either way, bandwagoning complicates the original theory's core prediction that states will always oppose the strongest actor.
Globalization and interdependence
Growing economic interdependence challenges the assumption that military power is the primary currency of international politics. Global trade networks, financial markets, and multinational corporations create forms of power and vulnerability that don't fit neatly into traditional balancing frameworks.
The rise of non-state actors (NGOs, terrorist organizations) and transnational threats (climate change, pandemics) further complicates the picture. These challenges often require cooperative responses that cut across the competitive, state-centric logic of balance of power theory.
Historical examples of balance of power
European balance of power (1815–1914)
After Napoleon's defeat, the great powers convened at the Congress of Vienna (1815) to construct a system designed to prevent any future bid for European hegemony. The resulting Concert of Europe relied on regular diplomatic conferences, flexible alliances, and a shared commitment to maintaining equilibrium among Britain, France, Austria, Prussia, and Russia.
The system preserved relative stability for much of the 19th century. But it gradually eroded as rising nationalism, imperial competition, and the formation of rigid alliance blocs (the Triple Alliance and the Triple Entente) replaced flexible diplomacy with inflexible commitments. The result was World War I, a catastrophic failure of the balance of power system. The key lesson: balance of power works best when alliances remain flexible. Once they harden into permanent blocs, the system loses its ability to adjust to shifting power dynamics.
Cold War bipolar balance
The Cold War (1945–1991) produced a bipolar system, with the United States and the Soviet Union each leading a bloc of allied states. The balance was maintained through nuclear deterrence (the doctrine of mutually assured destruction, or MAD), proxy wars in the developing world, and intense ideological competition.
Waltz argued that bipolarity was inherently more stable than multipolarity because each superpower only had to track one main rival, reducing the chance of miscalculation. The two superpowers did avoid direct military confrontation. But the rivalry fueled devastating regional conflicts (Korea, Vietnam, Afghanistan) and a costly arms race that consumed enormous resources on both sides.
Post-Cold War unipolar moment
The Soviet collapse left the United States as the sole superpower, creating what Charles Krauthammer called the "unipolar moment." This posed a puzzle for balance of power theory: why didn't other states immediately form coalitions to counterbalance American dominance?
Several explanations have been offered. Some point to soft balancing efforts (e.g., France and Russia opposing the 2003 Iraq War in the UN Security Council). Others argue that the relatively benign nature of American hegemony, combined with the institutional order the U.S. had built, reduced the incentive to balance. William Wohlforth argued that American power was simply so preponderant that balancing was impractical.
In any case, the rise of China, India, and other powers in the 21st century has moved the system toward greater multipolarity, and balancing dynamics are becoming more visible again.
Critiques of balance of power theory
Realist assumptions about state behavior
Critics argue that the theory's assumptions are too simplistic. Treating states as unitary, rational, security-maximizing actors ignores the messy reality of how foreign policy actually gets made. Leaders miscalculate. Bureaucracies have competing agendas. Ideology and identity shape threat perception in ways that pure power calculations can't capture.
Constructivists, in particular, argue that what counts as a "threat" is socially constructed, not objectively determined by the distribution of power alone. Alexander Wendt's famous point applies here: the U.S. doesn't balance against Britain (a nuclear-armed state) the way it balances against North Korea, because shared identity and norms shape how power is interpreted. Anarchy is what states make of it.
Neglect of domestic politics
Balance of power theory operates at the systemic level, focusing on the distribution of power among states while largely ignoring what happens inside them. Critics from the liberal and foreign policy analysis traditions argue this is a serious blind spot.
Public opinion, interest groups, regime type, and institutional constraints all shape how states respond to external threats. A democracy facing an election may be slower to mobilize for balancing than an authoritarian state with centralized decision-making. Integrating domestic-level variables would make the theory more realistic, but also more complex, and it would undermine the parsimony that neorealists like Waltz considered a strength.
Difficulty of measuring power
Power is notoriously hard to measure. It includes military capability, economic output, technological sophistication, diplomatic influence, and even cultural appeal. There's no agreed-upon formula for combining these dimensions into a single metric.
This creates real problems for the theory. If you can't accurately measure the distribution of power, you can't reliably predict when balancing will occur or whether the system is in equilibrium. GDP and military spending are common proxies, but they capture only part of the picture. A state's ability to convert resources into actual influence depends on factors like political cohesion, geographic position, and the quality of its leadership, none of which are easy to quantify. This measurement problem makes the theory difficult to falsify, which is a significant weakness from a social science perspective.