No proliferation impact.

Other analysts have sounded a much less alarmist tone, however. Some scholars even suggested that an Iranian bomb held great potential for stabilising an unbalanced and volatile Middle East (Waltz, 2012). Closer to the mainstream of Western strategic discourse, various experts have argued that despite the risks of proliferation, nuclear weapons, and the deterrent they provide should get (more) credit for contributing, in combination with other factors, to what has been labelled ‘the Long Peace’ among the great powers since 1945 (Gaddis, 1999, p. 268–271; Gavin, 2012a, p. 164; Acton 2010, pp. 16–17). Still others have contended that because nuclear proliferation is such a rare phenomenon, and since robust nonproliferation measures tend to be disruptive, the net destabilising effect of new nuclear countries is quite small and, therefore, manageable (Mueller 2010, pp. 95–99; Hymans 2013, pp. 293–296).

The question of whether nuclear proliferation has stabilising or destabilising effects is not just fascinating for scholars of the nuclear age, but also highly consequential for practical policy issues. For in order to debate the merits of particular policy choices – such as preventive military strikes against nuclear facilities, grand bargains with potential proliferators or complete nuclear disarmament – we need to understand first how the spread of nuclear weapons impacts regional and global security.

The chapter proceeds in three steps. The first section provides the foundation for the other parts by summarising what we know about empirical patterns of proliferation and the utility of nuclear weapons for statecraft. The second section then engages the literature on the consequences of proliferation, focusing in particular on how proliferation has influenced international stability. The final section explores whether some states have been more affected than others, and what measures these states have taken to prevent proliferation, or at least mitigate its negative consequences.

Patterns of nuclear proliferation and the utility of nuclear weapons

Nuclear proliferation is commonly defined as the spread of nuclear weapons to states that did not previously have them. Within a broader conceptual framework that is rarely used by scholars, yet popular in the arms control community, this diffusion of nuclear weapons to additional states is labelled horizontal proliferation. It is conceptually accompanied by the notion of vertical proliferation, which refers to qualitative improvements and increases in the number of nuclear weapons in the stockpiles of existing nuclear weapon states. In accordance with the typical usage of the term in the scholarly debate, this chapter focuses only on how the horizontal proliferation of nuclear weapons affects international stability.

One important empirical pattern that has shaped how nuclear proliferation is understood concerns the way in which nuclear weapons have spread. The word ‘spread’ appears to suggest that the established nuclear powers have provided other interested nations with (at least a few) operational nuclear warheads. Yet such transfers have never been undertaken. Certainly, states that sought nuclear weapons have often received significant assistance from other nations (Schofield, 2014; Fuhrmann, 2012), sometimes in the form of highly sensitive technologies (Kroenig, 2010). Nonetheless, since all these transfers remained well below the weapons threshold, nations seeking nuclear weapons always had to build them indigenously. Hence, in reality, the spread of nuclear weapons has meant that merely the ambition to possess a nuclear arsenal has spread to additional states, each of which then had to pursue that goal primarily through indigenous efforts.

Importantly, since a state’s national efforts to turn its desire for nuclear weapons into reality naturally span several (and sometimes many) years, nuclear proliferation must be conceived of as a process, as opposed to just a single step (Meyer, 1986). This point is reinforced by the fact that 29 out of 39 states that have embarked upon that path (Müller and Schmidt, 2010, p. 157; Mikoyan, 2012; Santoro, 2017) have not acquired a nuclear arsenal. Hence, a lot of nuclear proliferation activity has been undertaken by nations that did not ultimately become nuclear weapon states. Three patterns explain this situation.

First, owing not just to the technological, but also the institutional and managerial challenges of the task, some nations simply failed in their efforts to build the bomb (Hymans, 2012; Braut-Hegghammer, 2016). Second, a few countries have chosen a nuclear ‘hedging’ strategy, intentionally confining their efforts to developing the technological capability to build an arsenal quickly while refraining from exercising that option (Narang, 2016–17, p. 134). Third, several states have undertaken a ‘nuclear reversal’, abandoning their nuclear weapons activities before developing nuclear explosive devices (Müller and Schmidt, 2010).