The contribution of game theory to the study of International Relations (IR) has been both transformative and contested. Emerging from the works of John von Neumann and Oskar Morgenstern, the earliest formulations of game theory provided a mathematical framework to study strategic interaction among rational actors, a core feature of the international system. Since IR is characterised by anarchy, absence of a central authority, and constant dilemmas of cooperation, conflict, deterrence, signalling, bargaining, and uncertainty, game theory has become an essential tool to conceptualise how states behave when their choices depend on the choices of others. Scholars across traditions—Thomas Schelling, Robert Axelrod, Duncan Snidal, Kenneth Oye, Bruce Bueno de Mesquita, James Fearon, and others—have demonstrated that game theoretic models can illuminate a wide range of phenomena from nuclear deterrence to trade cooperation, from crisis bargaining to alliances, and from institutional design to war onset. The analytical depth produced by game theory stems from its ability to formalise assumptions, specify payoffs, model strategic reasoning, and derive equilibrium outcomes that reflect patterns of international behaviour.

The earliest and perhaps the most enduring influence of game theory on IR arose during the Cold War, when nuclear strategy required unprecedented levels of strategic calculation. Thomas Schelling, in his landmark works such as The Strategy of Conflict (1960) and Arms and Influence (1966), used game theoretic reasoning to explain how deterrence, compellence, and crisis bargaining operate under conditions where credibility and communication are central. Schelling demonstrated that deterrence is not merely about possessing weapons but about the credibility of threats, a point captured through models like the game of chicken, where states attempt to make their threats more credible by reducing their own room for manoeuvre. When two adversaries are locked in a situation where unilateral retreat is perceived as weakness and mutual escalation leads to disaster, the insights of game theory become critical. Schelling’s concept of “the threat that leaves something to chance” highlighted how uncertainty, rather than pure rationality, could stabilise deterrence by increasing the probability of inadvertent escalation, thereby making threats more believable. This reconceptualisation of nuclear strategy was a radical departure from earlier strategic thought and became foundational to U.S. and Soviet strategic planning.

Beyond nuclear issues, game theory has enriched the analysis of cooperation under anarchy, especially through models such as the Prisoner’s Dilemma, Stag Hunt, and Coordination games. Robert Axelrod’s celebrated work The Evolution of Cooperation (1984) used iterated Prisoner’s Dilemma tournaments to show that cooperation could emerge even among self-interested actors without central authority. His findings that “tit-for-tat”—a strategy that is nice, retaliatory, forgiving, and clear—outperforms others provided one of the strongest arguments for the possibility of sustained cooperation in the international system. It countered the earlier realist skepticism that cooperation is fragile and short-lived. Axelrod’s work inspired institutionalist scholars such as Robert Keohane and Kenneth Oye to elaborate how international institutions help states overcome problems of free-riding, information asymmetry, and uncertainty, issues that are central in collective action games. Oye’s typology demonstrated that whether cooperation emerges depends on payoff structures, iteration, uncertainty, and issue linkage, all of which can be formally grasped using game theory. This indicates how game theory not only provides analytic models but shapes theoretical debates within IR.

The ability of game theory to clarify strategic bargaining has been especially influential. James Fearon’s seminal contributions in the 1990s used game theoretic models to show why rational states might still go to war, despite war being costly and inefficient. Fearon identified three conditions—private information with incentives to misrepresent, commitment problems, and issue indivisibility—that could lead to bargaining failure. Game theory offered a formal apparatus to understand how misperception, signalling, and credibility problems generate conflict even when states would prefer negotiated settlements. Fearon’s model of “costly signalling” further demonstrated how states use mobilisations, audience costs, or diplomatic gestures to credibly convey preferences and resolve information asymmetries. These insights have reshaped the study of war by grounding explanations of conflict in rational strategic behaviour rather than irrationality or miscalculation. Indeed, much of the contemporary literature on crisis bargaining, compellence, and negotiation is deeply indebted to game theoretic logic.

In addition to conflict, game theory has enhanced our understanding of coalitions and alliances. Scholars like Mancur Olson applied collective action theory—rooted in game theoretic principles—to explain why larger states bear disproportionate burdens in alliances such as NATO. Since public goods are prone to free-riding, alliance dynamics often resemble multi-player Prisoner’s Dilemma or collective action games. Game theory clarifies how states calculate the costs of defection, evaluate the credibility of partner commitments, and develop mechanisms like side payments, host-nation support, or burden-sharing norms to stabilise alliances. By formalising these relationships, game theory reveals that alliances are not only responses to external threats but complex strategic arrangements with internal incentive problems.

The role of game theory is also prominent in international political economy. Trade negotiations, monetary cooperation, and regulatory harmonisation often involve strategic interdependence. The classic Heckscher-Ohlin or Ricardian models of trade do not capture these political dynamics, but game theory does so by analysing how states negotiate tariff reductions or form preferential trade agreements. Duncan Snidal’s contributions emphasised that while the Prisoner’s Dilemma captures many features of cooperation problems, issues such as trade or environmental regulation often resemble coordination games, where the challenge is not defection but choosing compatible standards. Game theory shows how distributional conflicts and strategic linkages shape bargaining outcomes. Similarly, in global environmental politics, models of common-pool resource games and public goods games explain why climate agreements are difficult to sustain and how mechanisms like issue linkage, punishment strategies, or side payments can help stabilise cooperation.

Another major contribution of game theory to IR comes from formal modelling of democracy, domestic politics, and foreign policy, particularly through the work of Bruce Bueno de Mesquita. His selectorate theory integrates domestic political incentives into international behaviour, using game theory to argue that leaders’ survival strategies shape decisions on war, sanctions, and negotiations. While controversial, his models demonstrated how formal theory can incorporate complex multi-level interactions, linking domestic political structures to international outcomes. Game theory has thus broadened the analytical lens of IR by allowing researchers to combine rational choice assumptions with domestic politics and institutional analysis.

One of the most significant strengths of game theory is its ability to formalise uncertainty, a constant feature of international politics. States rarely possess complete information about others’ preferences, capabilities, or intentions. Game theory introduces models of incomplete information, such as Bayesian games, where actors update beliefs on the basis of signalling, reputation, and past behaviour. This framework helps explain why states sometimes bluff, why credibility matters more than capability, and why misunderstandings can escalate crises. Scholars such as Robert Jervis and Charles Glaser have used game theoretic reasoning to illuminate the security dilemma, where states’ defensive measures appear threatening to others. Although not exclusively game theorists, their insights resonate with the logic of strategic interaction and belief updating central to game theory.

Despite its enormous influence, game theory has not been without criticism. Critics argue that its reliance on rational choice assumptions, pre-defined preferences, and mathematical abstraction limits its real-world applicability. Richard Ned Lebow, Alexander Wendt, and constructivist scholars argue that state behaviour is shaped not only by strategic calculation but also by identities, norms, historical context, and social construction of interests, factors that game theory does not adequately capture. Empirical validity remains a concern: models often predict equilibria that do not accurately reflect observed behaviour, leading some scholars to characterise game theory as “over-formalised.” Additionally, game theory tends to assume stable preferences, whereas real-world preferences evolve with domestic politics, leadership changes, and social pressures. Nonetheless, defenders argue that these critiques misunderstand the purpose of formal models: game theory does not seek to predict outcomes mechanically but to clarify the logic of strategic situations, thereby sharpening theoretical debates.

Furthermore, some scholars highlight that game theory’s heavy emphasis on conflict and rationality during the early Cold War period limited its ability to account for complex, long-term changes in the international system. The iterated Prisoner’s Dilemma shows that cooperation is possible, but its conditions—iteration, reciprocity, shadow of the future—are not always present in all issue areas. Even so, the flexibility of game theory allows scholars to adapt assumptions and incorporate new empirics. Recent works on network games, evolutionary game theory, and agent-based modelling have updated the framework, making it more dynamic and sensitive to learning processes, institutional evolution, and multi-actor interactions.

Despite limitations, the analytical contribution of game theory remains foundational. Its greatest strength lies in how it has transformed the language of IR: concepts such as payoffs, strategies, equilibria, signalling, commitment, credible threats, deterrence, free-riding, and collective action are now part of mainstream IR vocabulary. Even scholars who do not use formal models engage with these concepts when analysing state behaviour. Game theory has also increased the methodological rigour of IR, demanding clarity in assumptions, causal mechanisms, and logical coherence. It offers a way to uncover counterintuitive insights—for instance, that increased power can reduce security, that uncertainty can enhance deterrence, or that cooperation may require the possibility of punishment—providing guidance for both scholars and policymakers.

In sum, the contribution of game theory to the study of International Relations is profound, multi-dimensional, and enduring. It has shaped the understanding of strategic interaction, conflict and cooperation, nuclear deterrence, crisis bargaining, alliances, international institutions, trade negotiations, environmental agreements, and foreign policy decision-making. Through scholars like Schelling, Axelrod, Fearon, Bueno de Mesquita, Oye, and Snidal, game theory has penetrated diverse subfields of IR, offering methodological precision and analytical clarity. While critiques highlight its limitations in addressing normative, constructivist, or identity-based dimensions of international politics, game theory remains indispensable for studying situations where the choices of one actor depend critically on the choices of others. Its central insight—that international politics is fundamentally a realm of strategic interdependence—continues to help scholars interpret patterns of war, peace, cooperation, bargaining, and institutional design. Even as the international system evolves with new challenges posed by climate change, cyber warfare, and emerging technologies, game theory remains a robust and evolving analytical tool capable of explaining how states navigate complex strategic landscapes.