This paper shows why states, acting in their own self-interest, may create informational asymmetries that lead to war. In our models, two actors with no private information invest in military capacity before engaging in crisis bargaining. If bargaining fails, the states go to war, and the payoffs of a war depend on the two states' military capacities. We examine a large class of models and show that states have incentives to keep each other guessing about their exact levels of military capacity — even though doing so creates the risk of war. Thus, self interest and strategy are to blame for the emergence of uncertainty about military strength and war. Our paper explains two stylized facts: States devote considerable resources to secrecy in the national-security realm, and often disagree about the balance of capabilities.