In this article, we demonstrate that through their use as tools of military containment, sanctions play an unappreciated role in international politics. We show that sanctions can be used to smooth shifts in relative power that would otherwise lead to preventive war. After presenting a model of shifting relative power and sanctions, we discuss two cases in which sanctions were imposed to destroy an adversary’s military capability. We also explore the implications of this argument for the evaluation of sanctions’ effectiveness. Because sanctions may be deployed as a mechanism to lock in the status quo rather than revise it, the outcome of a sanctions episode must be compared to its counterfactual rather than the status quo ante. Our argument suggests that sanctions may be effectively deployed in response to expected adverse shifts in relative power; therefore observed outcomes disadvantageous to the sanctioning state are insufficient proof that sanctions have failed.