In the past four months, the war in Ukraine has brought the use of nuclear weapons into the realm of possibility in our lifetimes. We can say that all-out nuclear war is no longer only a theoretical possibility, and in the event of all-out nuclear war, all of humankind would be involved.
To follow Clemenceau's ironic quote about leaving war to the generals, the discussion of the escalation of nuclear use and nuclear deterrence strategy is too directly related to our lives for us to ignore it and leave it to military and security experts. In this article, I would like to examine the state of nuclear deterrence strategy as a story in which everyone can participate.
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The logic of mutually assured destruction, i.e., "No one will survive if a nuclear war starts because the nuclear powers will always be able to counterattack and destroy the other party if they are attacked by nuclear weapons. Therefore, no one will start a nuclear war," is dangerous. There is a vulnerability and a perversion in this logic. For analysis on conflicts such as nuclear deterrence in the framework of game theory, see Shelling (1960), Zagare (1992), and Kraig (1999).
First, in terms of its vulnerability, the logic of mutually assured destruction is correct in terms of game theory, but the assumptions that are necessary to reach the conclusions are too strong. The assumption is that under perfect information, the players have full knowledge of their opponent's behavioral objectives and that they will act fully rationally in accordance with their own behavioral objectives. In reality, however, such an assumption is completely untenable. The world has learned that information, intentions, and everything else about the Russian President Vladimir Putin's statements and actions are opaque, i.e., they are quite far from the above assumption.
In terms of a perversion in the logic of mutually assured destruction, the goal that is to be achieved via a conflict is out of proportion with the means to achieve it. In the logic of mutually assured destruction, the individual conflict between two countries, whose goal is "survival in the world," treats "the world itself" as a means (i.e., hostage) to that end. The balance between the goal (i.e., survival of individual nations in the world) and the means used to achieve it (i.e., destruction of the world itself) is not proportionate.
The following is a bad metaphor, but it is like saying that a gang that controls Tokyo and a gang that controls Osaka are fighting to expand their power, and if the Osaka gang is about to lose, they will kill all 20 million residents of the Tokyo metropolitan area who have nothing to do with the gang. Such a threat, if carried out, would make any goal (in this case expansion of the gangs' power) meaningless. In the first place, there is no legitimacy in establishing a framework of a game in which the parties to the conflict have the largely undisputed authority to determine the existence of the entire world, now that the Cold War is over. It is just as unjustifiable to assume that gangs have the right to kill or not kill entire populations of cities.
It is necessary to resolve such vulnerabilities and perversions and consider stable nuclear deterrence.
To overcome vulnerabilities, the nuclear powers must be stopped from ascending the ladder of nuclear escalation, because ascending the ladder of escalation will increase tensions and the likelihood of unforeseen events.
In order to overcome the perversion, it is also necessary to discuss the issue with a game that includes as players the entire world (the rest of the world (ROW) outside the parties to the conflict) that is unrelated to the conflict but would suffer tremendous damage from the use of nuclear weapons.
The ROW victims of the use of nuclear weapons are not merely those who are currently living in non-party countries. All future generations that will continue into the infinite future are victims, in the sense that dozens, hundreds, and thousands of generations that would have been born in the world may cease to exist. This is true not only for the human race, but also for every living thing on earth. Whatever the reason, purpose, or cause for the conflict between the two parties, it cannot justify the endangerment of the survival of future generations of humans and all living things on our planet.
For example, to mankind 2000 years in the future, the current invasion of Ukraine will seem like a completely pointless conflict, not worth risking the survival of humanity, just as the reasons for the Punic Wars 2000 years ago do not matter to us today.
For the entire world, therefore, the main goal is to prevent the conflicting parties from climbing the ladder of nuclear escalation.
This is merely a thought experiment, but as a mechanism to prevent some party from ascending the first step of a nuclear ladder, it would be beneficial to create a treaty that imposed sanctions for the preemptive use of nuclear weapons, to which many nations would become parties, that would "impose immediate, unconditional, and maximum sanctions against any nation that launched a nuclear preemptive strike.” In this case, sanctions would mean a broad range of sanctions by all non-military means. It would include not only economic sanctions, but also various enforcement measures, such as exclusion from international frameworks.
This is tantamount to establishing a new norm that "a nuclear preemptive strike, even a limited one, is a criminal act against humanity in that it endangers the survival of all human beings unrelated to the conflict in question.”
Note that the rejection of the preemptive use of nuclear weapons is completely incompatible with the current Japanese government's thinking. Although it is unlikely that the government will make such a proposal under the current circumstances, it is meaningful to discuss new norms for nuclear deterrence from a blank slate, including theoretical possibilities, in response to the tail risk of nuclear use.
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Let’s consider the effectiveness of the new treaty in a diagram. Figure 1 shows the usual two-party game of nuclear deterrence. In a conflict between nuclear powers A and B, A decides whether to launch a strike with limited use of nuclear weapons (LS) or not to strike (NS), then B decides whether to counterattack (C) or not (NC), and then A decides whether to counterattack (C) or not (NC). If both countries choose C, all-out nuclear war will result.
In this game, if both countries are rational, in equilibrium, State A implements limited nuclear use (LS), but State B does not counterattack (NC), and nuclear escalation does not occur. In theory, all-out nuclear war is avoided. In the real world, however, once limited nuclear weapon use occurs, various uncertainties spread, and the possibility of an all-out nuclear war is no longer zero.
Figure 2 shows what would happen if all countries in the world joined a treaty that imposed sanctions for the preemptive use of nuclear weapons. In this case, the gain that would result from a preemptive nuclear attack by State A would be negative because sanctions would be imposed by the rest of the world for its limited use of nuclear weapons. As shown in Figure 1, without sanctions, it would be impossible to stop the limited use of nuclear weapons by State A. However, as shown in Figure 2, if it is known in advance that countries around the world will impose sanctions on a nuclear-using State, State A will not use nuclear weapons first because there are no gains to be had from limited nuclear use in the first place. Thus, the first step in nuclear escalation is prevented. Since nuclear use will not occur in the equilibrium, sanctions will not be necessary, and as a result, the sanctioning countries will not incur any costs.
Although the Treaty on the Prohibition of Nuclear Weapons (TPNW) entered into force in 2021, the abolition of nuclear weapons is currently unrealistic because it cannot be achieved without the consent of all nuclear weapon possessing states. TPNW does not provide for sanctions against the use of nuclear weapons. If a treaty on the sanctions to preemptive use of nuclear weapons can be created, sanctions can be implemented even if the signatories are non-nuclear weapon states, so the creation of this treaty would create a new international norm with high credibility.
Creating the new treaty is essentially tantamount to the creation of an international norm of equity that all citizens in various countries in the world should share the power to decide the fate of this planet equally.
* Translated by RIETI with some additional information