Dealing with the threat posed by the proliferation of weapons of mass destruction (WMD) – usually taken to mean nuclear, biological, chemical weapons and their means of delivery – is now the top priority of US national security policy. There also is a deepening, if belated, recognition of the importance of preventing proliferation, that is, of taking steps to head off the acquisition of these weapons by terrorist groups or states in the first place. In large part, this new emphasis on preventing proliferation reflects a judgment, not only among traditional practitioners of non-proliferation but even more importantly among the defense and military communities, of the serious difficulties and very significant resource demands of countering the consequences of proliferation once it has occurred. Indeed, proliferation prevention or non-proliferation is now often referred to as the “sweet spot” for US actions.

A more robust and effective future proliferation prevention posture, however, needs to be grounded in a sound analytic framework or model for thinking about possible proliferation futures – and what could bring them about. Any such framework or model also will need to reflect and provide a means to encompass uncertainty writ large – that is, a mix of specific uncertainties, the unexpected, and simply “wild cards” that pervade the future of proliferation at several different levels. At the level of national decision making, uncertain and even idiosyncratic factors and processes sometimes drive proliferation decisions and choices.