What causes arms races between rival states? Traditional international relations theories view arms build-ups as deterrence motivated reactions to real or perceived threat. Research on the consequences of arms races, however, suggests that military build-ups can have unintended negative consequences. I offer an alternative explanation for arms race onset built on the assumption that leaders understand the potential costs of military build-ups and, consequently, wish to avoid arms races if possible. According to the model, states only engage in arms competitions when there are particularly salient stakes at risk. I posit and test a model arguing that territorial stakes, because of their inherent salience, represent the stakes most likely to produce arms races. Tests of the model on a population of rival states confirm the hypothesis.