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Forging Conventional Shields with Nuclear Swords:

How Nuclear Allies Shape Conventional Armament Decisions

J Andrés Gannon

Assistant Professor, Political Science

Vanderbilt University

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Question: why do states pursue some conventional capabilities, but not others?

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Answer

Conventional military capabilities are a function of the credibility of security guarantee from nuclear allies:

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Strong ally nuclear security guarantee →

  • Increase protege capabilities vs unconventional security threats
  • Decrease protege capabilities vs invasion, occupation, and conquest

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Roadmap

  1. Nuclear-conventional burden-sharing matters
  2. Credibility of nuclear security guarantees shapes how states arm
  3. Can identify patterns in 70 years of the US nuclear umbrella

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Existing State of the Art

Conventional aggression:

  • Assurances encourage allied aggression (Vasquez and Senese 2008, Lanoszka 2018)
  • Or assuage security concerns (Leeds 2003, Kim 2011)

Nuclear arming:

  • Assurances prevent allied proliferation (Reiter 2013, Monteiro and Debs 2014)
  • Or may be irrelevant (Goldstein 2000, Fuhrmann and Sechser 2014)

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But we don’t know how nuclear assurances impact conventional arming

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Theory: Nuclear Swords Forge Non-Nuclear Shields

Key Assumptions:

  1. Credible protection from nuclear-armed ally should improve protege security
  2. Improved security allows a state to alter defense resource allocation

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Theory: Nuclear Swords Forge Non-Nuclear Shields

Nuclear-armed ally provides a specific type of security

  • Nuclear protection credibly deters invasion and conquest

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That allows re-allocation of defense resources towards other types of security

  • States safe from invasion invest in security against unconventional threats

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Empirics: US alliances in Asia Pacific

Dependent variable: armament decisions of protege state

  • Capabilities dedicated to gray zone vs invasion/conquest

Independent variable: credibility of US nuclear security commitment

  • National security strategies

Sample: Japan, South Korea, Taiwan, Australia (1970 - present)

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Implications

“the forces that were on the cutting edge of action were the non-nuclear ones. Nuclear force was not irrelevant but it was in the background. Non-nuclear forces were our sword, our nuclear forces were our shield.”

- Robert McNamara on the Cuban Missile Crisis (1962)

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Credibility of US nuclear protection influences capabilities with which allies can fight