Nothing to Fear but Fear Itself? Nuclear Proliferation and Preventive War∗

When does nuclear counterproliferation succeed? When does it lead to preventive war? We argue that as the ratio between (i) the effect of nuclear acquisition on the balance of power and (ii) the costs of preventive war increases, counterproliferation becomes more successful but mistaken preventive wars also become more likely. We apply this logic to comparing the dynamics of proliferation during and after the Cold War. During the Cold War, the high costs of preventive war relative to the impact of nuclear acquisition on the balance of power made counterproliferation difficult, leading to the steady spread of nuclear weapons. After the Cold War, however, U.S. power preponderance slows proliferation down by lowering the costs of preventive war relative to the effect of nuclear acquisition on the balance of power. At the same time, mistaken preventive wars – such as, we argue, the Iraq invasion of 2003 – are more likely.