Causes of War — Analyze causes of war (commitment problems, information, bargaining) (intro-to-standard)

Historical Context & Motivation

War is among the most destructive and costly activities that states undertake, yet it has remained a persistent feature of international politics for millennia. For most of recorded history, scholars attributed war to human nature, the ambitions of individual leaders, or the inherent aggressiveness of particular regimes. These explanations, while intuitive, left a fundamental puzzle unresolved: if war destroys wealth, kills citizens, and weakens states, why do rational actors choose to fight rather than divide the contested goods peacefully? This question — often called the rationalist puzzle of war — became the organizing framework for a generation of international relations theory beginning in the late twentieth century.

The central question this lesson addresses is deceptively simple: given that war is costly, what prevents states from reaching a negotiated settlement that both sides prefer to fighting? The rationalist framework does not deny the importance of ideology, nationalism, or domestic politics; rather, it asks what strategic mechanisms must be present for these factors to actually produce armed conflict. By isolating these mechanisms — information problems, commitment problems, and bargaining indivisibilities — we gain analytical leverage over when and why wars begin.

Core Principles & Definitions

The rationalist framework begins with a deceptively straightforward premise: because war is costly, there should always exist a range of peaceful settlements that both sides prefer to fighting. This range is called the bargaining range. If State A expects to win a war with probability p and both sides pay costs c for fighting, then any division of the disputed good between p − c and p + c leaves both parties better off than war. The puzzle, then, is why states fail to locate a deal within this range. Three mechanisms explain this failure.

The Bargaining Range — A Visual Explanation

The core logic of the bargaining model can be visualized as a one-dimensional spectrum representing the full range of possible divisions of a disputed good. The diagram below illustrates how the bargaining range emerges from the intersection of each state's reservation point — the minimum outcome each prefers to the expected value of war.

As the diagram illustrates, the width of the bargaining range is c_A + c_B — the total costs of war borne by both sides. The higher the costs, the wider the range and the easier it should be to find a peaceful settlement. Conversely, when war is perceived as cheap or when one side drastically underestimates the other's costs, the range shrinks and the probability of bargaining failure rises. The critical insight is that the mere existence of a bargaining range does not guarantee peace; states must still be able to identify the range (an information problem) and commit to a deal within it (a commitment problem).

The Three Mechanisms in Depth

Mechanism 1: Private Information and Incentives to Misrepresent

In any crisis, each state holds private information about its own military capabilities, the resolve of its leadership, or the costs it is willing to bear. If this information were publicly known, the two sides could pinpoint the bargaining range and select a deal within it. The problem, however, is that states have strong incentives to misrepresent their private information. A state that reveals it is weak or irresolute invites the adversary to demand more; a state that credibly appears strong can push the settlement closer to its preferred outcome. Because cheap talk is not credible, the only way to convey resolve may be through costly actions — escalation, mobilization, or even limited strikes — that themselves raise the risk of full-scale war. This dynamic creates a tragic paradox: the very process of communicating to avoid war can trigger the war it was meant to prevent.

Mechanism 2: Commitment Problems

Even under complete information — where both sides know each other's capabilities and resolve perfectly — war can still occur if states cannot credibly commit to honoring agreements over time. The canonical scenario involves a shifting distribution of power. Suppose State B is rapidly growing in military strength. A deal struck today reflects today's balance of power, but State B, once stronger, will have every incentive to renegotiate on more favorable terms. State A, recognizing this, may calculate that fighting a preventive war now — while it still holds a military advantage — is preferable to accepting a deal that will erode as State B's power grows. The absence of an international sovereign capable of enforcing contracts means that states operate in a self-help system where promises about future behavior are inherently suspect.

Mechanism 3: Issue Indivisibility

The third mechanism posits that some goods at stake in international disputes cannot be meaningfully divided. Control of Jerusalem, for instance, carries profound religious and symbolic significance that resists compromise through partition or power-sharing. If the issue is truly indivisible, the bargaining range collapses to a single point, and no mutually beneficial deal exists. Most rationalist scholars, however, treat indivisibility with skepticism. Fearon argued that issue linkage — combining the disputed issue with other goods such as financial transfers, trade agreements, or territorial swaps — can restore divisibility. Empirically, truly indivisible issues are rare; what appears indivisible is often rendered so by domestic political incentives that make leaders unwilling to accept creative compromises, a point that blurs the line between rational and domestic-level explanations.

Classifying Wars by Mechanism

Understanding which mechanism drives a particular conflict is essential for policy prescription. A war caused by information failures might be prevented through transparency measures, confidence-building mechanisms, or mediation that helps states reveal credible information. A war driven by commitment problems, by contrast, requires institutional solutions — security guarantees, power-sharing agreements, or external enforcement — that make promises about future behavior credible. The following diagram maps prominent historical conflicts onto the three rationalist mechanisms, illustrating how the same analytical framework can illuminate very different empirical cases.

Worked Example: Applying the Bargaining Model

Consider a stylized scenario based on the pre-World War I rivalry between Germany and Russia. Both states are contesting influence over the Balkans, a contested sphere of influence we normalize to a value of V = 1. Germany believes it has a 60% chance of prevailing in a war (p = 0.6). The cost of war is c_G = 0.15 for Germany and c_R = 0.10 for Russia. We will trace through the bargaining model to identify the zone of agreement and explore how information asymmetries could cause breakdown.

Strengths and Limitations of Rationalist Explanations

The rationalist framework for war has profoundly shaped international relations scholarship since the mid-1990s, but it is not without significant critics. Evaluating both its strengths and limitations is essential for understanding where the theory provides genuine analytical traction and where alternative approaches — constructivist, psychological, or domestic-political — may be needed.

Connections to Advanced Theory

The introductory bargaining model presented in this lesson serves as a gateway to more sophisticated theoretical developments in international relations and political science. Several advanced research programs extend, challenge, or refine the core rationalist framework in important ways. Understanding these connections helps position the bargaining model within the broader theoretical landscape of conflict studies.

One particularly fertile area of development concerns the application of the bargaining framework to civil wars. Walter (2002) demonstrated that commitment problems are especially severe in intrastate conflicts because rebel groups must disarm to implement peace agreements, rendering themselves vulnerable to government reprisal. Unlike interstate settings where sovereignty provides some minimal guarantees, civil war settlements require external guarantors — peacekeeping forces, third-party mediators — to enforce compliance. This insight has had direct policy implications for UN peacekeeping operations and power-sharing agreement design in places like Bosnia, Sierra Leone, and South Sudan.

Practice Problems

Summary & Review