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April 8, 2022

Nuclear deterrence in armed conflicts
between nuclear-weapon and non-nuclear-weapon states:
The war in Ukraine

Tokuhiro Ikeda
(Director of National Security Institute, Fujitsu System Integration Laboratories / Senior Fellow, Asia Center, Harvard University / Vice Admiral (Ret.) JMSDF)

 In 1994, Dr. Barry Posen of MIT analyzed Ukraine’s defense strategy against Russia, with an eye to promoting denuclearization after the collapse of the Soviet Union.* His findings presented a defense concept against nuclear-weapon states for non-nuclear-weapon states, bearing in mind that Russia, as a nuclear-weapon state, is a non-nuclear Ukraine’s greatest security threat. When the pros and cons of denuclearizing Ukraine became a hot button issue in 1994, Posen’s treatise had a great deal of relevance. Issues raised in his paper not only have present-day relevance for the current war in Ukraine; they are also germane to current nuclear threats facing a non-nuclear Japan. I will outline a part of this paper, analyze the current situation in Ukraine, and consider Japan's nuclear strategy.

 At the beginning of his piece, Dr. Posen states:
 "I will argue that Ukraine can address most of its plausible threat scenarios, with modest effectiveness, through a military strategy that could be termed a 'strategic defense in depth.' This strategy cannot hope actually to hold all of Ukraine against all challenges, but it can pose an impressive array of probable costs and plausible risks to a future aggressor. If properly organized, Ukrainian forces should be able to fight a tough delaying action in the eastern half of the country.
 Ukrainian forces should then be able to mount a positional defense of the other half of the country, west of the Dnipro, against a very strong attack. This defense could impose very high costs on an attacker, though it too would ultimately fail if Ukrainian forces cannot produce or, more realistically, receive as military aid, the fuel, replacement weaponry, and munitions necessary to sustain modern warfare."

 Posen’s paper accurately predicted the current situation 28 years ago and describes a defense concept for non-nuclear-weapon states against nuclear-weapon states. The conclusions of this paper are examined below. I will give my opinion as a reference for proposals on Japan's nuclear strategy.

 Ukraine's military strategy against Russia can be premised on either (1) forward defense, (2) mobile defense, or (3) defense in depth. Defense in depth is the best strategy. Forward defense is a strategy to defend upfront a large-scale border, and requires a huge defense budget beyond Kyiv’s means. Mobile defense easily allows Russia to achieve its goals, provided they are limited.
 Ukraine’s ability to launch counteroffensives would be limited in such a scenario, as we have seen with Crimea. Defense in depth is a strategy to establish a line of defense with the Pripet Marshes to the North and the Dnipro River as main defensive lines, and to enable long-term resistance with the support of NATO and other Western countries. Conventional deterrence by Kyiv will make Moscow understand that Russia's invasion of Ukraine entails serious long-term strategic costs and great risks. (I believe this strategy is currently being carried out.)

 In his treatise, Dr. Posen argues that this strategy is the most reliable, while Ukraine's nuclear deterrence strategy should be considered as an alternative. He states that the weaknesses and strengths of a conventional strategy and a nuclear one must be systematically considered. Moreover, if Ukraine possesses nuclear weapons, it will certainly appear to have more deterrence capacity, but he argues that nuclear weapons do not seem to be a reliable deterrent when Russia pursues limited strategic goals. He concludes that nuclear weapons may provide more protection than conventional weapons, but at the cost of significant risk if the strategy fails.

 This treatise was written at a time when Ukraine was abandoning its nuclear weapons. It emphasizes that by providing necessary assistance to non-nuclear-weapon states like Ukraine, it is possible to defend a non-nuclear-weapon state even under threat from nuclear-weapon states by strengthening conventional forces.

 In the current situation, Russia has threatened use of nuclear weapons, but this appears little more than bluster. An exchange of views with researchers at Harvard Asia Center pointed out two signs of a Russian decision to use nuclear weapons. The first is withdrawal of Russian troops to the rear and the second is establishment of a Russian home-country defense system against retaliatory attacks. At present, Moscow has made no such moves, and it is unlikely that a nuclear attack will take place.

 Aside from the fact that a nuclear war is unlikely to occur, we need to analyze how Russian nuclear weapons affected its invasion of Ukraine. Posen's piece does not consider that Ukraine, a non-nuclear power, must protect its territory by sacrificing its population. His "defense in depth" strategy shows no consideration for civilians living east of the Dnipro River.

 I will now consider what Russia's strategic goals for the invasion of Ukraine were, and how nuclear weapons contributed to them.

 Regarding Russia's strategic goals, Dr. Posen's dissertation cites the following three points: (1) Recovery of Crimea, (2) conquering oblasts including Kharkiv, Luhansk, and Donetsk, and (3) conquering Ukraine east of the Dnipro River (35-40% of the total) including Kyiv. In addition to this, we must consider a fourth: not allowing former Soviet Union republics such as Ukraine to join NATO. A similar logic applies to Moldova and Belarus.

 The recovery of Crimea was achieved in 2014 when a unilateral treaty was signed between Russia, Crimea, and Sevastopol. Ukraine has argued that the UN General Assembly resolution to invalidate the annexation was adopted by a majority, but the annexation of Crimea has effectively become a fait accompli.

 Some believe that Russia's strategic goal for the current invasion of Ukraine is conquest of its eastern regions, but this may change to prevention of its entry into NATO. Russia has suffered extremely heavy casualties, but this strategic goal seems to have been achieved.

 Ukraine will not be able to easily announce its accession to NATO in the future, and Russia has achieved sufficient results for Moldova to recognize this. Moreover, NATO cannot expect any further eastern expansion.

 Dr. Posen said that if Russia was trying to achieve limited goals (e.g., conquest of oblasts including Kharkiv, Luhansk, and Donetsk), nuclear weapons would be not always an effective tool even if Ukraine had them. I question if that is really the case.

 From the viewpoint of deterring war, it is a fact that deterrence did not work and led to Russia invading. Ukraine, a non-nuclear state and a non-allied country, protecting its land at the expense of a large number of people is a tragic situation. Efforts to come under NATO's nuclear umbrella have not paid off. NATO proved reluctant to provide military support to Ukraine as a non-allied country in the face of a Russia that possesses vast nuclear weaponry. The intent was to avoid World War III, but the West had to limit its objectives due to Russia’s nuclear capabilities.

 Considering Russia's operational objective as in (2) above, i.e., the conquest of oblasts such as Kharkiv, Luhansk, and Donetsk, it seems that Ukraine will obstruct achievement of that goal. Deterrence did not prevent invasion for the following reasons: (1) President Putin underestimated the degree of resistance by Ukrainian conventional forces; and (2) despite claiming "integrated deterrence," the United States has stated from the beginning that it will not be involved in military operations. Because of this, Putin made a misjudgment that he could achieve his goals. However, considering that Russia is advancing its nuclear strategy with strategic and tactical nuclear weapons, the situation can be viewed in a completely different way, as mentioned above.

 From the above, it can be seen that non-nuclear-weapon states and non-allied nations are extremely vulnerable when nuclear-weapon states try to achieve their goals with a nuclear strategy. Fortunately, Japan has a strong alliance with the United States, a nuclear power. It goes without saying that we must continue striving to ensure the effectiveness of the United States' extended nuclear deterrence. Furthermore, it is necessary to consider concrete measures for ensuring effectiveness without being bound to Japan’s three non-nuclear principles. We must also think about what to do if extended nuclear deterrence does not work.

 It is easy to imagine that China, which aims to become another nuclear weapon state, will make full use of its nuclear strategy to achieve its goals. In readiness for that time, it is necessary to envision a strategy whereby allies are reluctant to use nuclear weapons in order to avoid World War III.

 The Ukrainian concept of defense defends the land at the expense of the people. Fortunately, Japan is an island country, and the sea and sky are natural defense lines, but we must specifically consider how to protect the people and the land.

Written by Dr. Barry Posen, Ford International Professor of Political Science (First published November 1994) A 1994 Defense Concept for Ukraine | 2022 | Publications | MIT Security Studies Program (SSP)

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