|Fig. 1: US and USSR Nuclear Stockpiles.  (Source: Wikimedia Commons)|
Mutually Assured Destruction (MAD) hinges on the idea of deterrence. A balance of power between opposing actors exists such that neither side has a rational incentive to initiate conflict and thus risk retaliation from an opponent.  This result is reframed in game theory as a Nash equilibrium between two or more powerful actors, where each player acts in their rational self-interest. Although exceptionally simple, MAD is critical to maintaining global stability especially between large hegemonic nations with developed nuclear programs like USA, Russia, and China. Notably, during the Cold War, both the US and USSR stockpiled on nuclear warheads (as shown in Fig. 1), ostensibly as a means of deterrence. Currently, nine nations possess nuclear weapons. Other state and non-state actors (e.g. terrorists) are trying to gain access to nuclear weapons.  While the Non Proliferation Treaty (NPT) has helped control the spread and use of nuclear weapons, countries like India, Pakistan, and North Korea have developed their programs outside of the NPT. [1,3]
As more players enter the MAD game, possible scenarios increase in number and complexity. When do the rules of MAD breakdown or fail to apply? Let us consider two primary exceptions, miscalculation and irrational actors, in which MAD does not yield desirable, peaceful outcomes.
Actors who cannot effectively evaluate risks and outcomes can destabilize the system away from its Nash equilibrium. As former secretary of defense William Perry explains, the false belief that an attack is imminent causes a country to miscalculate the risk of full-scale war and accidentally escalate a conflict to the nuclear level.  US and Soviet nuclear weapons are on hair-trigger alert, where the weapons are maintained on a ready-to-launch status. Weapons can be launched the moment a threat is perceived. 
A prime example of miscalculation occurred in 1983 where Russian satellite detection systems incorrectly perceived the launch of 5 US missiles. Fortunately, this did not result in any retaliatory measures, but it is easy to imagine how dire the consequences could have been.
Not all actors are rational. Furthermore, actors that generally act rationally can have lapses in judgement. Ideally, actors with nuclear weapons would require a consensus of multiple decision-makers before definitive and irreversible action is taken, which would diversify against the risk of one decision-maker acting irrationally. In some cases, especially in organizations where a single leader holds all the decision-making power, there is an exceptional risk for irrational decision making. Irrational actors also tend to also be extremist actors that lack methods of conventional discourse. In these cases, irrational actors mix their ideology, usually politically motivated, with religious extremism, resulting in counterintuitive, irrational actions such as suicide bombing.  Fortunately, most non-state terrorist organizations and state-sponsors of terrorism (such as Iran and Iran's Supreme Leader), where power tends to be highly concentrated into a single individual, do not presently possess nuclear capabilities.
© Sreyas Misra. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 J. Cartwright and V. Dvorkin, "How to Avert a Nuclear War," New York Times, 19 April 15.
 S. Nunn, On Nuclear Weapons, Nations Must Cooperate to Avoid Catastrophe," Washington Post, 26 May 16.
 D. H. Joyner, Interpreting the Nuclear Non-Proliferation Treaty (Oxford University Press, 2011).
 "Reducing the Risk of Nuclear War: Taking Nuclear Weapons off High Alert," Union of Concerned Scientists, January 2016.
 R. S. Norris and H. M. Kristensen, "Global Nuclear Stockpiles, 1945-2006," Bulletin of the Atomic Scientists 62, No. 4, 64 (2011).