That the anarchic system generates incentives for states to balance each other's power is conventional wisdom in international relations. As such, the contemporary unipolar system is an anomaly.  Observers explain its existence in several ways, including the benevolence of U.S. hegemony and the constraints international institutions impose on the exercise of U.S. power.  None of them, however, explain what is perhaps the most puzzling outcome of the Soviet collapse:  the decision of the United States to maintain its level of military spending. To explain its choice, we extend the seminal argument Waltz advanced long ago to a dynamic setting. Using a simple model, we show that the interest of the unipole in deterring a challenge to its power can induce it to continue to invest in guns rather than to shift its resources to the production of butter. This strategy can enable the incumbent unipole to preempt the balancing process that has long been thought to be central to state survival under anarchy.