The dominant explanation for why nuclear weapons have remained unused since 1945 is deterrence, an explanation routinely mentioned in almost any text on the role of nuclear weapons during the Cold War. In this chapter I critique this explanation, along with several other competing explanations for the non-use of nuclear weapons, on both theoretical and empirical grounds. I then introduce the taboo argument and outline the role of a nuclear taboo in inhibiting the use of nuclear weapons by the United States since 1945. I lay out a framework for evaluating the influence of the taboo in terms of three effects of norms and three pathways by which norms have effects. I then review the leading theories of norm formation and offer a model of how the nuclear taboo developed.

It is often noted that studying non-events – such as the non-use of nuclear weapons – poses special challenges for analysis. It would seem especially difficult to identify the causes of something that did not happen. Yet the study of important non-occurrences is central to the study of international politics (and social life in general, for that matter). We study why revolutions did not occur in some countries, why the debt crisis of the 1980s did not bring the international monetary system down, why the Cold War did not become a hot war, or why ethnic conflict does not break out in some regions.