Since the beginning of the nuclear age, 37 states are known to have once started nuclear weapon activities. Of these, five are recognized as the "official" nuclear weapon states, four more are de facto nuclear weapon possessors, and the end of the Iranian story remains to be completed. However, 26 states have terminated their nuclear weapon programs (though in the present situation, some of them might be tempted to revive them).
That doesn’t enforce the realist notion of a linear nuclear proliferation process that is getting worse and worse. This paper explores the reasons why so many states who embarked on nuclear weapon programs chose eventually to forego them. The "usual suspects" are tested as independent variables: alliance guarantees, economic and technical capabilities, regime norms, the nuclear arms race, democratic processes and liberalization. The paper finds that alliance guarantees as well as economic and technical capabilities exert a surprising small influence on nuclear decisions. Far more significant factors are domestic regime structure and regime norms, especially the normative impact of the NPT.
Müller, Harald & Schmidt Andreas (2010): The Little Known Story of De-Proliferation: Why States Give Up Nuclear Weapon Activities, in: Potter, William C. Potter & Mukhatzhanova, Gaukhar (eds.): Forecasting Nuclear Proliferation in the 21st Century. The Role of Theory, Volume 1, Stanford University Press, Stanford, pp. 124–158.