International relations (IR) as a field seeks to explain how states interact in an anarchic global system. Among the competing theoretical perspectives, Realism has historically dominated the study of IR due to its focus on power, conflict, and the constraints imposed by human nature. Rooted in the works of Thucydides, Machiavelli, and Hobbes, realism emphasizes that international politics is primarily a struggle for power and survival among self-interested states. Unlike idealism or liberalism, which stress cooperation, morality, and international law, realism portrays a world characterized by anarchy, insecurity, and competition. Classical realists, particularly Hans J. Morgenthau, elaborated a systematic framework to understand IR based on enduring principles of political behavior. Morgenthau’s six principles of political realism have become foundational to both theoretical and practical analyses of global politics.

Realism and International Relations

Realism explains international relations through several interrelated assumptions. Firstly, it posits that states are the principal actors in global politics, operating in an anarchic system where no overarching authority can enforce rules or mediate disputes. This anarchic environment compels states to prioritize national interest, often defined in terms of power and security, over moral or ideological considerations. As Morgenthau (1948) observes, political action is rooted in human nature, which he regards as inherently flawed and power-seeking (animus dominandi). This assumption suggests that conflicts are inevitable, and cooperation is temporary and contingent on overlapping interests.

Secondly, realism emphasizes the primacy of power in international affairs. Power is multifaceted, encompassing military capability, economic resources, political influence, and technological strength. States continually seek to maximize their relative power to ensure survival and prevent domination by others. This focus on relative rather than absolute gains distinguishes realism from liberal theories that highlight mutual benefits and interdependence. For instance, during the Cold War, the United States and the Soviet Union engaged in a zero-sum competition, exemplifying the realist notion that power accumulation often triggers rivalry rather than collaboration.

Thirdly, realism accounts for state behavior through rationality and strategic calculation. States are assumed to be rational actors, capable of assessing threats, weighing costs and benefits, and taking actions that safeguard their security and national interest. However, the realist lens also recognizes the limits of rationality imposed by uncertainty, misperception, and the dynamic distribution of power, which often leads to security dilemmas and unintended escalation.

Finally, realism explains international conflicts as natural outcomes of structural constraints and human behavior. Wars, alliances, and diplomacy are interpreted as instruments to balance power, deter aggression, and preserve autonomy. For example, the balance of power politics in 19th-century Europe demonstrates how states form coalitions to prevent domination, a concept central to realist theory.

Morgenthau’s Six Principles of Political Realism

Morgenthau’s six principles provide a systematic framework for understanding state behavior and international politics:

1. Politics is governed by objective laws rooted in human nature
   Morgenthau argues that political behavior is not random but follows patterns derived from human nature, which is inherently self-interested and power-seeking. This principle underlines the psychological and ethical dimensions of politics, asserting that states, like individuals, act to secure their interests. Critics, however, argue that this principle is overly deterministic, ignoring cultural, institutional, and ideological factors that shape state behavior. For instance, the post-World War II cooperation in Europe through institutions like the European Union challenges the idea that states always pursue power at the expense of morality.
2. Interest defined in terms of power
   According to Morgenthau, the national interest of a state is primarily expressed in terms of power—military, economic, or political. This principle explains why states engage in wars, alliances, and competition. The realist lens interprets policies such as the U.S. containment of the Soviet Union as a rational pursuit of national interest. However, critics contend that reducing interest solely to power oversimplifies international relations, neglecting normative, economic, and environmental concerns increasingly salient in global politics.
3. Universal and timeless nature of political laws
   Morgenthau contends that the laws of politics are consistent across time and space due to the enduring nature of human behavior. This principle allows realism to generalize about the inevitability of power struggles. Yet, critics highlight that historical changes, technological innovation, and globalization introduce variables that challenge the universality of these laws. The digital revolution and cyber warfare illustrate new domains of power that classical realism did not foresee.
4. Autonomy of politics
   Politics is autonomous from morality, economics, or religion, meaning that ethical prescriptions cannot override the imperatives of national interest. While this principle clarifies why states often act pragmatically in foreign policy, it attracts ethical criticism. Realist strategies, such as support for authoritarian regimes for strategic gain, raise moral dilemmas and questions about the legitimacy of foreign policy decisions. The U.S. support for authoritarian allies during the Cold War exemplifies this tension.
5. Political realism is aware of moral significance but rejects universal moral laws
   Morgenthau acknowledges that political action has moral consequences but argues that no universal moral framework can guide state behavior. States operate under a pragmatic ethic of survival and interest. This principle highlights the tension between ethics and power, yet some scholars argue that it risks justifying aggression and neglecting human rights, particularly in contemporary international law regimes emphasizing Responsibility to Protect (R2P).
6. Politics must be evaluated pragmatically, not ideologically
   Realism emphasizes the practical assessment of power and interest over ideological goals or utopian visions. Policies should be judged by their effectiveness in securing national objectives, not moral purity. This principle provides analytical rigor for evaluating historical events, such as the Munich Agreement or détente policies, but it faces critique for potentially normalizing unethical or coercive behavior in international politics.

While Morgenthau’s principles offer a coherent framework, several limitations emerge. Firstly, the anthropocentric focus on human nature has been criticized for being reductionist, ignoring systemic, cultural, and economic structures that shape international outcomes. Secondly, the overemphasis on power risks neglecting cooperative dynamics, multilateralism, and transnational issues such as climate change, which require collaborative solutions. Thirdly, the detachment of politics from morality can lead to a cynical worldview that condones realpolitik at the expense of ethical governance.

However, the relevance of Morgenthau’s realism persists, especially in explaining conflicts driven by security concerns, territorial disputes, and power imbalances. The Ukraine-Russia war, the U.S.-China strategic competition, and the Iran nuclear issue demonstrate the continued utility of a realist framework in understanding state behavior under anarchy. Moreover, realist principles can be complemented by other approaches such as liberal institutionalism or constructivism to address non-material factors and ethical dimensions.

In sum, realism explains international relations as a domain characterized by anarchy, power struggles, and the pursuit of national interest. Morgenthau’s six principles provide a foundational blueprint for analyzing state behavior, emphasizing the centrality of power, the inevitability of conflict, and the pragmatic nature of politics. While the framework faces criticism for ethical limitations, historical determinism, and neglect of non-material factors, it remains analytically powerful for interpreting persistent patterns of international conflict and competition. A nuanced understanding of IR requires integrating realism’s insights with contemporary developments, recognizing that power politics and moral considerations are often intertwined in shaping the global order.

“The tragedy of great power politics lies in the logic of survival itself,” observed John J. Mearsheimer. Realism, the most influential approach in International Relations, views world politics as a struggle for power among self-interested states in an anarchic international system. Within this broader realist framework, Offensive and Defensive Realism represent two significant strands of Neorealism (Structural Realism). Both share the assumption that the international system is anarchic and that states are the principal actors seeking survival, but they diverge sharply on the question of how much power a state must pursue to ensure its security.

Defensive Realism: The Logic of Security

The roots of Defensive Realism lie in Kenneth Waltz’s Theory of International Politics (1979). Waltz argued that while anarchy compels states to be self-reliant, the rational pursuit of security—not endless accumulation of power—is the primary goal of states. States, he asserted, act as “security maximizers” rather than “power maximizers.” Excessive power accumulation provokes counter-balancing coalitions by other states, thereby reducing the aggressor’s security — a dynamic known as the security dilemma. Hence, defensive realists emphasize restraint, balance of power, and deterrence as the most stable strategies for survival.

A classical example of defensive realism can be seen in the U.S. policy of containment during the Cold War, which sought to check Soviet expansion without aggressive territorial ambitions. As Waltz wrote, “The first concern of states is not to maximize power but to maintain their positions in the system.” For defensive realists, stability arises when states adopt moderate policies that maintain systemic balance.

Offensive Realism: The Logic of Power Maximization

In contrast, John J. Mearsheimer, in his influential work The Tragedy of Great Power Politics (2001), advanced the theory of Offensive Realism, arguing that the best way for a state to ensure its survival is to become the most powerful actor in the system. Since no state can ever be certain about others’ intentions, Mearsheimer contends that states must act aggressively to maximize relative power and, if possible, achieve regional hegemony. Anarchy thus drives states toward competition and expansion rather than equilibrium.

Offensive realism portrays world politics as a zero-sum game, where the gain of one state is perceived as the loss of another. Historical examples include Nazi Germany’s expansion in the 1930s, or the United States’ post-1945 dominance aimed at shaping global institutions and ensuring strategic primacy. Mearsheimer famously remarked, “The best way to ensure your survival is to be the most powerful state in the system.”

While both theories share the assumption of anarchy, they differ in their interpretation of how states respond to it. Defensive realists advocate caution and balance, believing that excessive ambition invites resistance, whereas offensive realists argue that dominance itself guarantees security. Thus, both represent two sides of the same structural logic — one highlighting moderation, the other expansion. In simple terms, if Defensive Realism is about managing power, Offensive Realism is about accumulating power.

Criticism and Relevance

Both strands of realism face criticism for their structural determinism — they underplay domestic politics, leadership perceptions, and the role of ideas, which constructivists like Alexander Wendt highlight. Their neglect of international institutions and norms, emphasized by neoliberal institutionalists such as Keohane and Nye, limits their explanatory scope in the post-Cold War world. Furthermore, the empirical validity of offensive realism has been questioned, as Mearsheimer’s predictions of renewed European conflict after 1990 did not materialize. Both also face ethical critiques for ignoring the role of morality, justice, and human rights in global politics.

Yet, their relevance persists. In an era of U.S.–China rivalry, Russia’s assertiveness in Ukraine, and India’s strategic balancing, states continue to oscillate between cautious restraint and assertive power projection. This confirms that despite globalization and interdependence, the realist logic of survival through power and prudence remains central to international relations.

In essence, Offensive and Defensive Realism capture the dual nature of the international system — the tension between security and power, restraint and ambition. Waltz’s Defensive Realism reminds states of the stability that comes from balance, while Mearsheimer’s Offensive Realism warns that only power can guarantee survival. Together, they reflect the enduring truth of realism: that in an anarchic world, the pursuit of security inevitably drives the competition for power — a tragic but inescapable logic of global politics.