We have recently witnessed the ftieth anniversary of the bombing of Hiroshima and Nagasaki, the only use of nuclear weapons in warfare. The non-use of nuclear weapons since then remains the single most important phenomenon of the nuclear age. Yet we still lack a full understanding of how this tradition arose and is maintained and of its prospects for the future. The widely cited explanation is deterrence, but this account is either wrong or incomplete. Although an element of sheer luck no doubt has played a part in this fortuitous outcome, this article argues that a normative element must be taken into account in explaining why nuclear weapons have not been used since 1945. A normative prohibition on nuclear use has developed in the global system, which, although not (yet) a fully robust norm, has stigmatized nuclear weapons as unacceptable weapons of mass destruction. Without this normative stigma, there might have been more ''use.'' 1 This article examines this phenomenon in the context of the nuclear experience of the United States.This investigation is motivated by several empirical anomalies in the conventional account-deterrence-of the non-use of nuclear weapons since 1945. First is the non-use of nuclear weapons in cases where there was no fear of nuclear retaliation, that is, where the adversary could not retaliate in kind. This anomaly includes the rst ten years or so of the nuclear era, when the United States possessed rst an absolute nuclear monopoly and then an overwhelming nuclear advantage over the Soviet Union. It also includes non-use by the United States in Vietnam (where the United States dropped tonnage equivalent to dozens of Hiroshima bombs) and in the 1991 Persian For helpful comments and criticisms on presentations of this article, I am grateful to participants in seminars at

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This article responds to key methodological and theoretical challenges posed by the literature on the role of ideas in international relations, especially the literature on ideas and the end of the Cold War. The article develops a theoretical framework that guides the analysis of the empirical articles that follow. It identifies explanatory strategies for the role of ideas and seeks to clarify key methodological issues in the study of ideas. The article defines terms, identifies several different relationships between ideational and material factors, and lays out a series of “tests” for evaluating the causal effect of various kinds of ideas and ideational mechanisms. It then seeks to clarify two primary issues: whether it is possible to draw a clearer line between the material and the ideational; and what is meant by “constitutive effects” and “constitutive explanation.” The article defends the notion of constitutive explanation and shows how both causal analysis and constitutive analysis are valid explanatory strategies for the role of ideas.

Why have nuclear weapons not been used since Hiroshima and Nagasaki in 1945? Nina Tannenwald disputes the conventional answer of 'deterrence' in favour of what she calls a nuclear taboo - a widespread inhibition on using nuclear weapons - which has arisen in global politics. Drawing on newly released archival sources, Tannenwald traces the rise of the nuclear taboo, the forces that produced it, and its influence, particularly on US leaders. She analyzes four critical instances where US leaders considered using nuclear weapons (Japan 1945, the Korean War, the Vietnam War, and the Gulf War 1991) and examines how the nuclear taboo has repeatedly dissuaded US and other world leaders from resorting to these 'ultimate weapons'. Through a systematic analysis, Tannenwald challenges conventional conceptions of deterrence and offers a compelling argument on the moral bases of nuclear restraint as well as an important insight into how nuclear war can be avoided in the future.

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