Mutual Optimism and Choosing to Fight

In this paper we argue that mutual optimism is not a valid explanation for war. Specifically, we ask if it is the case that war occurs if and only if mutual optimism occurs and if it is the case that the presence of mutual optimism is necessary for a positive probability of war. We show that in models in which either side can choose to fight, the answer to both of these questions is no. Thus, in a wide range of models, including the standard bargaining model of war, mutual optimism is neither always necessary or sufficient for war. War can occur without mutual optimism and mutual optimism can occur without war. ∗Associate Professor, Department of Political Science, 109E Harkness Hall, University of Rochester, Rochester, NY 14627. phone: 585.275.5810, email: [email protected]. †Assistant Professor, Department of Politics, 033 Corwin Hall, Princeton University, Princeton, NJ 08544. phone: 609.258.2960, email: [email protected].