We will now analyze the changes in nuclear deterrence with regard to the validity of deterrence in the Post-Cold War era through a two steps evaluation: we will first examine it in the context of a nuclear attack and then we'll move to its evaluation in a scenario of non-nuclear attack.
It appears to be true that, despite the enormous changes in the threat of nuclear attacks since the Cold War, the threat of such aggression is still the most effective - if not the only - mean to prevent nuclear attacks themselves: that is indeed the idea of a second-strike capability. Additionally, to extended deterrence, it is necessary to additionally implement the deterrence strategy and that is to be done with the aim of preventing the horizontal nuclear proliferation, namely the number of actors equipped with nuclear weapons. It is a reality that the expansion of the nuclear club has enhanced the possibility of a nuclear attack, differently from its vertical proliferation: it is consequent therefore that the likelihood of an offence may not depend on the numerical growth of warheads within a single Country, but rather on the number of Countries owning such kind of weapons. In line with a neorealist point of view, it is arguable that the more countries will have a nuclear capability, the more will enact an effective deterrence strategy and therefore the safer the world will be, in the constant fear of a nuclear war. What this theory does not consider is the current security scenario, in which actors do not behave in accordance with the schemes adopted during the Cold War: terrorist groups, to name a particular kind of player in this match, are paradoxically no longer acting according to the rationality or the common sense of the US or the USSR and it is for such reason that a deterrence strategy, to be effective, also has to include the prevention of horizontal proliferation. Therefore, starting from the assumption of a loss of rationality, how can deterrence be still a valid strategy in the Second Nuclear Age? The answer lays in the shifting from capability to credibility, as stressed by Lowther: in order to allow nuclear powers to effectively respond to irrational actors with a strategy of deterrence, it is necessary for the latter to believe that traditional rational actors will also be willing to employ nuclear weapons as well.
On the contrary, in the intra-states relationships, no much difference can be appreciated since the Cold War and both the traditional Super Powers keep pursuing a highly costly policy of expenditures for nuclear weapons: China, differently, does not employ a similar capital, enabling the Country to simply keep a minimal level of deterrence, strategy which many lobbies are actually working to obtain in the US as well. What remains as common in the First and the Second World Nuclear Areas is that the US and Russia both base their strategic nuclear weapons on the other and consequently their expenditures and investments in such area - to make a realistic prevision - are not going to be reduced in recent times.
Concerning the role of nuclear deterrence in non-nuclear attacks, that is usually applicable to those countries not being part of the traditional circle of nuclear powers, thus representing a change since the Cold War. Those countries have mostly violated the Non-Proliferation Treaty, but never faced a direct military attack, as we have significant reason in believing that the root cause behind that lays in their nuclear capability: their nuclear deterrence strategy is therefore perfectly in function. North Korea, in contrast with Iraq, is the perfect evidence for the aforementioned. Differently from the latter, North Korea has a more bothersome and developed policy, for what concerns the proliferation of WMDs, but it might be that thanks to its very deterrence strategy the Country has never faced a NATO attack. The role of nuclear deterrence is although relevant even at a regional level when considering conventional attacks, as displayed in the case of the conflict between India and Pakistan: it is only for their nuclear arsenals that the two enemies, like the US and the Soviet Union before them, did not enter into a direct conflict.
To conclude, it is safe saying that, with regard to the international security scenario, the relevance of nuclear deterrence has not changed. It is rather the strategy with which it is adopted to have suffered some changes, as we have analysed through this paper. The use of nuclear deterrence to counter traditional threats has remained constant during the years, particularly with regard to the two classical Superpowers, and, as we have seen, many changes have been adopted in order to adapt such weapons to more recent issues, terrorism being the most prominent.
With the evolution of times, entering new historical eras, it is evident that the contemporary security scenarios have required an evolution of deterrence, in order for the latter to remain st least as effective as it was. It is on such evolution that I would like us to stress our attention: the concept of nuclear deterrence has unquestionably evolved, but it is at the same time clear that, despite the previously mentioned difficulties of a possible Second Nuclear Age, it has been all but abandoned by the main actors of world security.Serena Carassale