Defeat mechanisms are strategies for achieving victory over an opponent. Although defeat mechanisms often rely on influencing the opponent psychologically and emotionally, most simulations of warfare do not model these "soft" factors, they model only victory by attrition. To create more accurate, adaptable, and believable systems, we must be able to model a variety of defeat mechanisms. We propose a model where parameters and attributes that affect emotional and physical fatigue, are combined to produce an overall measure of fatigue called effective fatigue. Effective fatigue, along with an agent’s state, is combined by a defeat model to produce probabilities of surrender. We create warfare scenarios involving catastrophe and surprise, and then examine the model’s behavior under these scenarios. We conclude with a discussion of how the model is related to our own Capture the Flag wargaming system.