Realism

Realism is the oldest and most influential school of thought in international relations theory. Its intellectual lineage stretches from Thucydides in ancient Athens through Machiavelli in Renaissance Florence to modern theorists like Hans Morgenthau and Kenneth Waltz. Its central claim is deceptively simple: in a world without a supreme authority above states, power is the ultimate currency of politics, and survival is the primary goal of every nation. This proposition has shaped foreign policy from Bismarck’s Germany to Cold War America to contemporary debates about China’s rise.

Realism’s enduring influence stems from its apparent explanatory power. The theory claims to account for recurring patterns across millennia of international history: why states balance against threats, why alliances form and dissolve, why hegemonic powers rise and fall, why peace remains fragile even among states with no desire for war. Critics charge that realism is too pessimistic, too narrow, or too dangerous—a self-fulfilling prophecy that creates the very conflicts it claims to explain. Yet even critics must grapple with realism’s core insights. The theory remains indispensable for understanding how states actually behave in a competitive world.

The Anarchic System¶

The foundation of realist thought rests on a single structural observation: there is no world government. Unlike domestic politics, where a state monopolizes legitimate violence and enforces contracts, the international system lacks any comparable authority. This condition—what realists call anarchy—does not mean chaos or disorder. It means that states cannot appeal to a higher power when threatened. They must provide for their own security.

The distinction is fundamental. Within a well-ordered state, if a citizen is threatened by a neighbor, they can call the police. Courts enforce contracts; laws prohibit violence; the state maintains order. International politics has no equivalent. When one state threatens another, there is no police to call, no court to appeal to, no authority to enforce agreements. The United Nations Security Council exists, but it lacks independent enforcement capacity, and the great powers possess vetoes precisely to ensure the UN cannot constrain their vital interests.

This structural reality produces predictable behaviors regardless of states’ internal character or leaders’ intentions. States arm themselves, form alliances, and view each other with suspicion—not necessarily because their leaders are evil, but because the system rewards caution and punishes naivety. A state that fails to attend to its security may not survive to regret the oversight. The history of Poland, partitioned three times and erased from the map for over a century (1795-1918), stands as a reminder of what happens to states that cannot defend themselves.

Anarchy does not imply perpetual war. States cooperate, trade, and maintain peace for extended periods. But cooperation under anarchy is always conditional, always fragile, always shadowed by the possibility that today’s partner may become tomorrow’s threat. Treaties can be broken; alliances can dissolve; circumstances can change. The wise statesman prepares for the worst while hoping for the best.

Core Assumptions¶

Realist theory rests on several interlocking premises that together constitute a distinctive worldview:

States as primary actors. While corporations, international organizations, terrorist groups, and transnational movements matter, realists insist that states remain the decisive players in world politics. Only states command armies capable of large-scale warfare, control territory, exercise sovereignty, and bear ultimate responsibility for their citizens’ survival. The United States can deploy carrier battle groups; Apple cannot. Russia can invade its neighbors; Gazprom cannot. This does not mean non-state actors are irrelevant—the 9/11 attacks demonstrated their capacity for disruption—but the responses that matter most come from states. Al-Qaeda’s attack produced state responses: the invasion of Afghanistan, the reorganization of American security apparatus, the transformation of international counterterrorism cooperation.

Rationality under uncertainty. States are assumed to act rationally in pursuit of their interests, calculating costs and benefits and choosing strategies likely to advance their security and power. This is not a claim that leaders are wise or that decisions are always correct—history overflows with blunders—but that states generally respond to incentives in predictable ways. The critical complication is uncertainty. States operate with incomplete information about others’ capabilities, intentions, and resolve. Is China’s military buildup defensive or offensive? Will Russia accept a diplomatic solution or push for more? Will allies honor their commitments when tested? This uncertainty itself generates security competition, as states hedge against worst-case scenarios they cannot rule out.

Power as the medium of politics. Influence in international affairs flows primarily from material capabilities—military force, economic resources, technological advantage, geographic position. A state’s voice in world politics is largely proportional to its power; weak states must accommodate the strong or seek protectors. Ideas and institutions matter, realists acknowledge, but often as reflections of underlying power distributions. International law constrains the weak more than the strong. International institutions serve the interests of the powerful states that created them. When institutions conflict with vital interests, states ignore or subvert them. The League of Nations could not stop Japan in Manchuria, Italy in Ethiopia, or Germany in the Rhineland. The United Nations could not prevent the Iraq War. Norms against territorial conquest did not stop Russia in Crimea. Power, not law, determines outcomes when fundamental interests clash.

Self-help as the organizing principle. Because no authority guarantees their survival, states must ultimately rely on their own capabilities. Alliances are expedients, valuable but not to be trusted absolutely. Britain and France were allies in 1914 and 1939; they had been enemies in 1815 and rivals throughout the 19th century. The United States and Soviet Union were allies against Hitler; they were adversaries within two years of victory. Today’s partner may be tomorrow’s rival; circumstances change, interests diverge, and alliances dissolve. The prudent state maintains the capability to stand alone if necessary. To do otherwise—to depend entirely on others for security—is to gamble survival on factors beyond one’s control.

The Intellectual Tradition¶

Realism claims the longest pedigree in international thought, tracing its lineage to the origins of Western political reflection.

Thucydides (c. 460-400 BCE), the Athenian historian of the Peloponnesian War, is often called the first realist. His account of Athens’s conflict with Sparta emphasizes power, fear, and interest as the drivers of state behavior. The Melian Dialogue, in which Athenian envoys tell the neutral islanders that “the strong do what they can and the weak suffer what they must,” encapsulates the realist worldview. Thucydides showed that even democratic Athens, the supposed beacon of civilization, behaved brutally when power permitted and interest demanded.

Niccolò Machiavelli (1469-1527), the Florentine diplomat and philosopher, is realism’s second founding father. Writing amid the Italian city-states’ constant warfare and foreign invasions, Machiavelli advised princes to focus on power rather than morality, on what is rather than what ought to be. “A man who wishes to profess goodness at all times will come to ruin among so many who are not good.” His ruthless counsel—better to be feared than loved, know when to break faith, use force and fraud as circumstances require—earned him centuries of condemnation and the adjective “Machiavellian.” But his insights into power politics remain uncomfortably relevant.

Thomas Hobbes (1588-1679) provided realism’s philosophical foundation. In Leviathan, Hobbes argued that without a sovereign to enforce order, humans exist in a “state of nature” characterized by the “war of all against all.” Life in this condition is “solitary, poor, nasty, brutish, and short.” For Hobbes, the solution was the social contract: individuals surrender their freedom to a sovereign who maintains peace. But the international system has no such sovereign. States exist in the Hobbesian state of nature, each pursuing its survival in perpetual competition.

Classical and Structural Variants¶

The modern realist tradition encompasses several distinct schools that share core assumptions but differ on crucial questions.

Classical Realism¶

Classical realism, the dominant form through the mid-20th century, locates the drive for power in human nature itself. Its foremost exponent was Hans Morgenthau (1904-1980), a German-Jewish refugee who became the most influential international relations theorist of his generation.

Morgenthau’s Politics Among Nations (1948) remains the foundational text of the discipline. Its core argument is that “international politics, like all politics, is a struggle for power.” The “concept of interest defined in terms of power” provides the master key to understanding foreign policy across cultures and eras. Whether examining Athenian imperialism, Roman expansion, European balance-of-power diplomacy, or Cold War competition, the same basic dynamics recur because human nature does not change.

Classical realists acknowledge that leaders pursue various goals—security, prosperity, prestige, ideology—but argue that power is the necessary means to all ends. A state without power cannot protect its citizens, advance its values, or achieve any other objective. Politics therefore inevitably becomes a struggle for power, regardless of actors’ ultimate purposes.

Classical realism also emphasizes the limits of rationality. Leaders are subject to passion, pride, and miscalculation. They pursue glory and prestige beyond any rational security requirement. They blunder into wars they could have avoided and miss opportunities for peace. The statesman’s art lies in navigating these treacherous waters, pursuing national interest with prudence and restraint, avoiding both reckless ambition and naive idealism.

Structural Realism (Neorealism)¶

Structural realism (or neorealism), developed by Kenneth Waltz (1924-2013) in Theory of International Politics (1979), shifts the explanation from human nature to systemic structure. Waltz’s innovation was to derive realist conclusions from the international system’s anarchic structure rather than from assumptions about human nature.

The key insight is that anarchy—the absence of a central authority—creates a “self-help” system. States cannot rely on others for their security; they must provide it themselves. This structural condition produces security competition regardless of leaders’ personalities or states’ internal character. Even a world populated entirely by status quo powers—states seeking only to preserve what they have—would experience arms races, alliance formation, and conflict, because none can be certain of others’ future intentions.

Waltz’s structural approach claims greater theoretical rigor than classical realism. By focusing on systemic variables rather than unit-level factors (leadership, ideology, regime type), neorealism generates predictions applicable across different historical contexts. The theory predicts that states will balance against threatening concentrations of power, that bipolarity is more stable than multipolarity, and that hegemonic bids will provoke countervailing coalitions.

Within structural realism, a crucial debate divides defensive and offensive variants:

Defensive realism (Waltz, Stephen Walt, Charles Glaser) argues that states generally seek security rather than power maximization. The international system, while competitive, provides incentives for restraint. Expansion is often counterproductive: it provokes balancing coalitions that leave the aggressor worse off than before. Napoleon’s France, Wilhelmine Germany, Nazi Germany, Imperial Japan, and the Soviet Union all pursued hegemony and were defeated by opposing coalitions. The system punishes overreach; wise states recognize these dynamics and pursue moderate policies. Security, not power maximization, is the rational goal.

Offensive realism (John Mearsheimer) contends that the only truly reliable path to security is hegemony—the elimination of all potential challengers. Since states can never be certain they have “enough” power, and since today’s potential threat may become tomorrow’s actual enemy, rational actors seek to maximize their relative position whenever opportunity permits. Great powers are “power maximizers, not security maximizers.” The tragedy is that this pursuit of security through dominance creates the very conflicts that make the international system dangerous. States that seek only to be safe end up threatening each other precisely because they seek safety through strength.

Mearsheimer’s The Tragedy of Great Power Politics (2001) argues that this logic applies particularly to great powers—states with sufficient resources to bid for regional or global dominance. Great powers cannot be content with the existing distribution of power; they must constantly seek to improve their position at others’ expense. This produces not occasional conflicts but endemic great power competition.

The Security Dilemma¶

One of realism’s most powerful and unsettling concepts is the security dilemma: actions taken by one state to enhance its security—building weapons, forming alliances, strengthening defenses—often make other states feel less secure, prompting them to respond in kind. The result is an arms race or heightened tensions even when no party intended aggression or harbored offensive designs.

The mechanism is straightforward. State A, fearing potential threats, increases its military budget. State B, observing A’s buildup, cannot be certain whether A’s intentions are defensive or offensive. Prudence requires B to assume the worst and increase its own capabilities. A now observes B’s response, concludes that its original fears were justified, and increases its efforts further. The cycle continues, with each side’s defensive measures appearing threatening to the other.

The Cold War exemplified this dynamic. The United States and Soviet Union each viewed the other’s military buildup as threatening. The Soviet Union, devastated by World War II and encircled by American bases, sought defensive buffers. The United States, confronting Soviet expansion in Eastern Europe, perceived aggressive intent. The result was a nuclear arms race that peaked at over 70,000 warheads—enough to destroy civilization many times over—that neither side truly wanted but neither could safely avoid.

The security dilemma helps explain why peace can be fragile even among states with no desire for conquest. It shows how war can result from fear rather than ambition, from misperception rather than malice. States may arm, ally, and ultimately fight not because they seek others’ territory but because they fear for their own survival. This tragic dynamic—security-seeking behavior producing insecurity—is one of realism’s most important contributions to understanding international conflict.

Some scholars argue that the security dilemma can be mitigated. Arms control, confidence-building measures, defensive military postures, and transparent communication can reduce misperception and break the cycle of escalation. Others are more pessimistic: the fundamental uncertainty about intentions cannot be eliminated, and states cannot safely assume others’ benign purposes. The debate continues, but the concept itself remains central to understanding why international relations are so prone to conflict.

Realism and Great Power Politics¶

Realism finds its natural application in the study of great power competition—the high-stakes interactions among states capable of reshaping the international order. The theory claims to explain why great powers rise and fall, why hegemonic transitions are dangerous, and why international politics exhibits recurring patterns despite vast changes in technology, ideology, and culture.

The rise of China and the persistence of Russian revisionism have renewed interest in realist frameworks after the post-Cold War period’s brief flirtation with liberal triumphalism. The “end of history” proclaimed in 1989—the supposed permanent victory of liberal democracy and market economics—looks increasingly premature. Great power competition has returned, and realism offers a framework for understanding it.

For offensive realists like Mearsheimer, China’s ascent poses a structural challenge to the United States regardless of Beijing’s ideology or intentions. China’s GDP has grown from less than 10% of America’s in 1990 to approximately 75% today; its military budget has increased correspondingly. A peer competitor in Asia threatens American primacy, and Washington will resist that challenge just as it resisted Soviet power. The nature of the regimes matters less than the distribution of capabilities. A democratic China would pose similar challenges; a reformed Russia would still be a great power with interests that clash with America’s. The Thucydides Trap—the historical pattern in which rising powers and established powers tend toward war—frames the contemporary debate.

Defensive realists offer a more nuanced view. China’s rise need not lead to war if both sides exercise restraint and avoid the destabilizing effects of the security dilemma. Geography matters: the Pacific Ocean provides natural buffers that make conquest difficult. Nuclear weapons make direct great power war potentially suicidal. Economic interdependence raises the costs of conflict. International institutions, whatever their limitations, provide forums for communication and face-saving compromises. But even defensive realists acknowledge that great power transitions are historically dangerous. The shift from British to American hegemony was peaceful; the shift from British hegemony to German challenge was not. Which pattern the US-China competition will follow remains uncertain.

Realism also illuminates current tensions with Russia. Moscow’s interventions in Georgia (2008), Ukraine (2014, 2022), and Syria (2015) reflect classic realist logic: a great power protecting its perceived sphere of influence, resisting the expansion of a rival alliance (NATO), and demonstrating that it remains a force to be reckoned with. NATO expansion, from a realist perspective, was bound to provoke Russian resistance regardless of Western intentions. Expanding a military alliance toward Russia’s borders, incorporating former Soviet republics, and promoting “color revolutions” in Russia’s neighborhood—these actions, however justified on other grounds, challenged vital Russian interests. Realists warned of this dynamic for decades; events have vindicated their analysis, even as they deplore the violence Russia has employed.

Critiques and Limitations¶

Realism’s parsimony is both its strength and weakness. The theory’s focus on a few key variables—anarchy, power, self-help—generates clear predictions but may oversimplify a complex world. Critics from various perspectives challenge realist assumptions:

Liberalism argues that realism underestimates cooperation. International institutions, trade interdependence, and shared norms have enabled sustained cooperation among states, particularly in Europe since 1945. The European Union’s very existence challenges the realist assumption that anarchy precludes deep integration. Former enemies—France and Germany, Poland and Germany—have achieved a peace so stable that war between them is literally unthinkable. Trade, investment, and institutional ties create mutual dependencies that raise the costs of conflict far beyond any potential gains. Democratic states, liberals argue, rarely if ever fight each other, suggesting that regime type matters in ways realism cannot explain.

Constructivism argues that realism neglects ideas and identity. Anarchy, constructivists contend, is “what states make of it.” The meaning of power depends on social context; American nuclear weapons mean something different to Canada than to North Korea. Identities shape interests: Germany today pursues different goals than Germany in 1914 not because the distribution of power has changed but because German identity has been transformed. Norms evolve: territorial conquest, once routine, is now internationally condemned. Slavery, colonialism, and great power war have become increasingly unacceptable. These changes cannot be explained by power distributions alone.

Domestic politics theories argue that realism’s unitary actor assumption is misleading. Foreign policy emerges from domestic political contests, bureaucratic interests, coalition dynamics, and leadership psychology. Democracies may behave differently than autocracies; populist leaders may reject rational calculation; interest groups may capture policy for narrow purposes. The same structural pressures produce different responses depending on domestic factors realism ignores.

Critical theorists charge that realism is ideological. By treating power politics as inevitable—“the way things are”—realism legitimizes existing hierarchies and forecloses alternatives. Realism may be a self-fulfilling prophecy: if leaders believe competition is inevitable, they will act competitively, producing the very conflicts the theory predicts. The theory serves the interests of powerful states and elites who benefit from the existing order.

Historical critiques note realism’s predictive failures. Realism did not predict the peaceful end of the Cold War, the rise of the European Union, or the long peace among great powers since 1945. If the theory cannot explain these transformations, its explanatory power is limited.

Realists respond to these critiques vigorously. Cooperation occurs, they acknowledge, but it remains fragile and dependent on underlying power balances. European integration was possible only under American security guarantees; remove those guarantees, and competition would return. The “democratic peace” may be an artifact of American hegemony rather than a fundamental law of international politics. Ideas matter, but they matter most when they align with power; idealistic projects unsupported by force routinely fail. The Soviet Union collapsed not because of ideas but because it could no longer compete economically and militarily. And the relative peace since 1945 owes much to American hegemony—a distribution of power, not a transformation of politics.

The debate between realism and its critics continues and is unlikely to be resolved. Each approach captures important aspects of international politics while neglecting others. The prudent analyst draws on multiple perspectives rather than committing exclusively to one.

Contemporary Relevance¶

Realism’s relevance surged after 2014, when Russia’s annexation of Crimea and China’s assertiveness in the South China Sea shattered assumptions about the “end of history.” The post-Cold War era’s optimism—the belief that globalization, democracy, and international institutions had fundamentally transformed world politics—gave way to a grimmer recognition that great power competition had never truly ended. The geopolitical lens returned to the center of strategic discourse.

Today, realist concepts inform debates across the most pressing issues in international affairs:

Great power competition between the United States and China dominates strategic discussion. China’s GDP has grown from $360 billion in 1990 to over $17 trillion today; its military spending has increased correspondingly. The First Island Chain, the Taiwan Strait, the South China Sea—these geographic flashpoints are analyzed through realist frameworks of power, deterrence, and balance. Whether the US-China competition can be managed peacefully or will end in conflict is perhaps the central question of contemporary geopolitics. Realists offer frameworks for thinking about this challenge, even as they disagree about likely outcomes.

NATO expansion and the war in Ukraine have vindicated realist warnings. Mearsheimer and other realists argued for decades that expanding NATO toward Russia’s borders would provoke a hostile response, regardless of the alliance’s defensive character. The 2022 invasion of Ukraine proved them tragically right. This does not justify Russian aggression—realists analyze behavior, they do not endorse it—but it demonstrates that power politics did not end with the Cold War. Russia, like other great powers, will resist encroachment on its perceived sphere of influence.

The limits of international institutions in restraining revisionist powers have become apparent. The UN Security Council cannot act against permanent members who possess vetoes. International law condemns aggression but cannot prevent it. Economic sanctions impose costs but rarely change behavior on matters states consider vital. The international order, realists argue, depends ultimately on the willingness and ability of status quo powers to enforce it—a distribution of power, not a set of rules.

The Indo-Pacific balance has become the focus of American strategy. The Quad, AUKUS, enhanced deployments to Japan and the Philippines, partnerships with Indonesia and Vietnam—these initiatives reflect classic balancing behavior against a rising power. Whether this approach will deter Chinese expansion or accelerate conflict is debated, but the logic is unmistakably realist.

Deterrence and nuclear risks have returned to prominence. Russia’s nuclear threats during the Ukraine war, North Korea’s expanding arsenal, China’s nuclear modernization, and the erosion of arms control agreements have raised concerns about nuclear stability not seen since the Cold War. The logic of deterrence—preventing war through the credible threat of unacceptable retaliation—is fundamentally realist, as is the recognition that deterrence can fail with catastrophic consequences.

Whether one accepts realism’s worldview or not, its concepts—anarchy, the security dilemma, the balance of power, hegemony, spheres of influence—remain indispensable tools for understanding international politics. Policymakers may reject realism’s pessimism; they cannot ignore its insights. Even critics must engage with realism, if only to explain why they believe the theory incomplete or dangerous. In a world of returning great power competition, the oldest tradition in international thought has proven disturbingly relevant.

Sources & Further Reading¶

History of the Peloponnesian War by Thucydides — The ancient foundation of realist thought, demonstrating through the Melian Dialogue that “the strong do what they can and the weak suffer what they must.”
Politics Among Nations by Hans Morgenthau — The foundational 1948 text of classical realism, establishing the concept of “interest defined in terms of power” as the key to understanding international politics.
Theory of International Politics by Kenneth N. Waltz — The 1979 work that transformed realism by shifting focus from human nature to systemic structure, launching the neorealist research program.
The Tragedy of Great Power Politics by John J. Mearsheimer — The definitive statement of offensive realism, arguing that great powers must maximize relative power to ensure survival.
The Origins of Alliances by Stephen M. Walt — Introduces “balance of threat” theory as a refinement of classical balance of power, explaining when and why states form alliances.