Arms control and the balance of power are seemingly mutually contradictory processes. They share a subtle relationship that can produce either peace or war, a relationship that depends largely on how uncertainty is managed. Certainty plays a vital role in arms control because it permits a regularity of interaction that promotes co–operation among states. Uncertainty plays an equally vital role in the balance of power by restraining states through the fear of third–party interference. As the degree of uncertainty decreases when a system tends toward bipolarity, so arms control becomes more salient. Consequently, the balance of power will likely contribute disproportionately more than arms control in a multipolar environment than in a bipolar one. An important consequence of this relationship is that there are circumstances where a successful arms control agreement may actually increase the likelihood of war by impairing the restraining influence of the balance of power.