In this paper we examine whether mutual optimism can be supported as a cause of war in models that permit the unilateral use of force. Previous work (Fey and Ramsay, 2007) has demonstrated that war cannot occur in any game in which both sides must agree in order to fight. With the more realistic assumption that either side can unilaterally use force, however, war is possible in equilibrium. But we show that mutual optimism is still not a valid explanation for war, because it is neither always necessary or sufficient for war in a wide range of models. In particular, we show that this is true for a broad class of models with unilateral force as well as bargaining models