Under the Umbrella: Nuclear Crises, Extended Deterrence, and Public Opinion

• Author: David M. Allison,Stephen Herzog,Jiyoung Ko
• DOI: http://doi.org/10.1177/00220027221100254
• Published date: 01 November 2022
• Date: 01 November 2022
• Subject Matter: Articles

Article

Journal of Conf‌lict Resolution

2022, Vol. 66(10) 1766–1796

© The Author(s) 2022

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DOI: 10.1177/00220027221100254

journals.sagepub.com/home/jcr

Under the Umbrella: Nuclear

Crises, Extended Deterrence,

and Public Opinion

David M. Allison

1

, Stephen Herzog

2

, and Jiyoung Ko

3



Abstract

How robust is public support for extended nuclear deterrence in patron and client

states? Recent studies have improved scholarly understanding of US public opinion

about nuclear weapon use against non-nuclear adversaries. Yet, there is limited

knowledge of public attitudes regarding retaliation for nuclear strikes against US allies.

We develop a theoretical typology of nuclear crises and investigate this phenomenon

with a novel survey experiment (n= 6,623). Americans, Japanese, and South Koreans

viewed realistic emergency alert messages about a most-likely case for nuclear re-

taliation: a North Korean missile attack on a US ally protected by the nuclear umbrella.

Support for nuclear retaliation is low in all three countries, with important cross-

national differences. Favorability increases with North Korean nuclear f‌irst-use, but it

remains limited nonetheless. Surprisingly, US “tripwire”troop casualties do not in-

crease Americans’demands for nuclear retaliation. These f‌indings have important

implications for the study of nuclear crises and practice of extended deterrence.

Keywords

nuclear weapons, nuclear umbrella, extended deterrence, alliances, security

guarantees, public opinion, survey experiment, foreign policy

1

Political Science, Yale University, New Haven, CT, USA

2

Center for Security Studies, ETH Zurich, Zurich, Switzerland

3

Political Science and International Relations, Korea University, Seoul, Republic of Korea

Corresponding Author:

StephenHerzog, Center for Security Studies,ETH Zurich, Haldeneggsteig 4, IFW, 8092Zurich, Switzerland.

Email: stephen.herzog@sipo.gess.ethz.ch

Introduction

Since the early atomic age, Washington has protected many allies against regional

threats. This policy of extended deterrence often involves US pledges to defend

partners with nuclear weapons, resulting in coverage by the “nuclear umbrella.”During

the Cold War,these assurances mai nly focused on deterring Soviet military invasions of

Western Europe, but they also sought to counter China and North Korea. Today’s

umbrella covers dozens of US allies confronting nuclear and non-nuclear threats

emanating from China, Iran, North Korea, Russia, and beyond. There are no explicit

requirements for US nuclear weapon use when red lines are crossed, but the nuclear

umbrella creates such expectations. A long-standing consensus among Washington

foreign policy elites holds that the umbrella deters bellicose rivals, dampens odds of

nuclear proliferation among US allies, and thus contributes to global peace and stability

(Fuhrmann 2018).

However, the North Korean nuclear crisis has raised concerns about the strength of

Washington’s security commitments. The Democratic People’s Republic of Korea

(DPRK) has tested six nuclear devices and 173 ballistic missiles at the time of writing,

including a suspected thermonuclear detonation and missile overf‌lights of Japan

(Herzog 2018,8;Nuclear Threat Initiative 2022). North Korean Supreme Leader Kim

Jong-un has claimed the ability to strike Japan, South Korea, and the continental United

States with nuclear weapons. Former US President Donald Trump responded to threats

against the United States with prospects of nuclear retaliation (Baker and Choe 2017),

but he showed markedly more restraint regarding threats toward Japan and South

Korea. Trump even considered withdrawing US troops from East Asia and suggested

these allies might be better off if they developed their own nuclear arsenals (Landler

2018). Perhaps this should be expected, as extended deterrence faces a daunting

paradox. As the severity and credibility of threats to US prot´

eg´

es increase, so too does

the level of risk presented to the United States and its population by intervening. Such

threats have not disappeared with Trump’s departure; North Korea continues to test

ballistic missiles and refuses to engage in nuclear diplomacy with the administration of

President Joe Biden (Kim 2021). The Pentagon has also continued joint military

exercises with South Korea, which are highly provocative to Pyongyang (Bernhardt

and Sukin 2021).

Public opinion will play a signif‌icant role in an emerging nuclear crisis involving

an attack on a US ally for two reasons. First, miscalculations could endanger

millions of American lives and citizens in allied nations. Second, Washington has

many bilateral security treaties and informal arrangements calling for consultations

in regional crises, irrespective of the target of an adversary’s attack. American

decision-makers are likely to take a strategic pause when possible to consider

different responses and sources of reputational costs: domestic audiences who may

hold leaders accountable for conf‌lict escalation and foreign audiences who may demand

Washington uphold its deterrent promises or lose credibility. Both the opinion of the US

Allison et al. 1767