Using a simple formal model, I argue for extrinsic uncertainty, archetypified as a sunspot, as a quasi-rationalist explanation for war. A sunspot is a random variable that has no effect on any of the fundamentals of the international system: not the distribution of resources, nor the countries' preferences, nor the technology of militarization, nor the technology of conflict. Nevertheless, war can transpire with sunspots and not transpire without them, so that sunspots cause war in a strictly counterfactualist sense. The phenomenon works through the mechanism of self-fulfilling prophecy: some of the countries think that sunspots matter, so they wind up mattering. The result obtains even when the countries are armed with objective and correct probabilities about sunspots and rational expectations about what happens within each sunspot-realized world. An empirical test confirms the result.
Department of Political Science Florida State University 531 Bellamy Building Tallahassee, FL 32306