C O R P O R A T I O N MICHAEL J. MAZARR, NATHAN BEAUCHAMP-MUSTAFAGA, TIMOTHY R. HEATH, DEREK EATON What Deters and Why The State of Deterrence in Korea and the Taiwan Strait For more information on this publication, visit www.rand.org/t/RR3144 Library of Congress Cataloging-in-Publication Data is available for this publication. ISBN: 978-1-9774-0400-8 Published by the RAND Corporation, Santa Monica, Calif. © 2021 RAND Corporation R® is a registered trademark. Cover: U.S. Army photo by Staff Sgt. Keith Anderson Limited Print and Electronic Distribution Rights This document and trademark(s) contained herein are protected by law. This representation of RAND intellectual property is provided for noncommercial use only. Unauthorized posting of this publication online is prohibited. Permission is given to duplicate this document for personal use only, as long as it is unaltered and complete. Permission is required from RAND to reproduce, or reuse in another form, any of its research documents for commercial use. For information on reprint and linking permissions, please visit www.rand.org/pubs/permissions. The RAND Corporation is a research organization that develops solutions to public policy challenges to help make communities throughout the world safer and more secure, healthier and more prosperous. RAND is nonprofit, nonpartisan, and committed to the public interest. RAND’s publications do not necessarily reflect the opinions of its research clients and sponsors. Support RAND Make a tax-deductible charitable contribution at www.rand.org/giving/contribute www.rand.org Preface This report documents research and analysis conducted as part of a project entitled What Deters and Why: North Korea and Russia, sponsored by the Office of the Deputy Chief of Staff, G-3/5/7, U.S. Army. The purposes of the project were (1) to provide the Army with improved and new frameworks for evaluating the deterrence of aggressor activities for both interstate aggression and aggression short of that threshold and (2) to apply those two frameworks to assess the United States’ conventional and nonconven- tional deterrence relationships with Russia and North Korea. In the latter case, for com- parative purposes, the authors also examine U.S. efforts to deter Chinese aggression. The research and writing for this report were completed in mid-2019. Events and developments since that time are not captured in this narrative. However, although some facts may have changed or new circumstances developed, we believe that the general interpretations, findings, and recommendations remain valid. This research was conducted within RAND Arroyo Center’s Strategy, Doctrine, and Resources Program. RAND Arroyo Center, part of the RAND Corporation, is a federally funded research and development center (FFRDC) sponsored by the United States Army. RAND operates under a “Federal-Wide Assurance” (FWA00003425) and com- plies with the Code of Federal Regulations for the Protection of Human Subjects Under United States Law (45 CFR 46), also known as “the Common Rule,” as well as with the implementation guidance set forth in U.S. Department of Defense (DoD) Instruction 3216.02. As applicable, this compliance includes reviews and approvals by RAND’s Institutional Review Board (the Human Subjects Protection Committee) and by the U.S. Army. The views of sources utilized in this study are solely their own and do not represent the official policy or position of DoD or the U.S. government. iii Contents Preface ................................................................................................. iii Tables ..................................................................................................vii Summary .............................................................................................. ix Acknowledgments ..................................................................................xiii Abbreviations .........................................................................................xv CHAPTER ONE Foundations for the Analysis and Outline of the Report ..................................... 1 CHAPTER TWO The State of Deterrence in Korea .................................................................. 5 North Korea’s Motivation ............................................................................. 6 Clarity of the U.S. Deterrence Message ............................................................14 Credibility of the U.S. Deterrence Message....................................................... 24 Conclusion ............................................................................................ 38 CHAPTER THREE The State of Deterrence in Taiwan ...............................................................41 China’s Motivation ................................................................................... 42 Clarity of the U.S. Deterrence Message ........................................................... 48 Credibility of the U.S. Deterrence Message........................................................53 Conclusion ............................................................................................ 56 CHAPTER FOUR Conclusions and Implications for the U.S. Army ..............................................57 Deterrence in Korea ...................................................................................57 Deterrence in Taiwan .................................................................................58 APPENDIX U.S. Deterrence of China in Three Taiwan Elections .........................................61 References .............................................................................................83 v Tables S.1. State of Deterrence in Korea ............................................................. x S.2. State of Deterrence in Taiwan .......................................................... xi 1.1. Key Variables in Interstate Deterrence ................................................. 2 2.1. Variables Related to North Korea’s Motivation ......................................15 2.2. Variables Related to the Clarity of the U.S. Deterrence Message for Korea ..... 24 2.3. Variables Related to the Credibility of the U.S. Deterrence Message for Korea ..................................................................................37 3.1. Variables Related to China’s Motivation ............................................. 48 3.2. Variables Related to the Clarity of the U.S. Deterrence Message for Taiwan ....52 3.3. Variables Related to the Credibility of the U.S. Deterrence Message for Taiwan ............................................................................... 56 A.1. Summary of Deterrence Variables for Three Taiwan Presidential Elections .....81 vii Summary The research reported here was completed in July 2019, followed by security review by the sponsor and the Office of the Chief of Public Affairs, with final sign-off in March 2021. In an era of intensifying strategic competition, the challenge of deterrence is becom- ing increasingly relevant—and, thus, so is the issue of what factors cause deterrence to succeed or fail. This question prompted a two-year research agenda for the U.S. Army. In earlier work connected to the same project, RAND Corporation researchers con- ducted a quantitative analysis of 39 cases of U.S.-led extended deterrence since 1945 and derived 12 variables that tend to determine whether extended deterrence policies succeed or fail (see Table S.1). In this report, we apply those variables to two ongoing examples of extended deterrence: U.S. efforts to deter North Korean aggression against South Korea and U.S. efforts to deter Chinese aggression against Taiwan.1 Our analysis leads us to conclude that the state of interstate deterrence in Korea is healthy. The United States and its ally South Korea (officially the Republic of Korea) have a robust military presence on the peninsula that, at a minimum, would make any effort by North Korea (officially the Democratic People’s Republic of Korea) to reunify the nations by force extremely costly and, more likely, would bloodily rebuff such an attempt and result in ending the Kim family’s rule. The deterrent effect of this military presence is enhanced by the fact that the bulk of it is provided by indigenous South Korean military personnel who are committed to defend their homeland. The United States has also communicated its willingness to defend South Korea against such an attack on numerous occasions, at the highest levels, and in unambiguous terms. As shown in Table S.1, we judged that all of the variables for deterrence in Korea are robust or effective. The color-coding in the table and in Table S.2 represents our judgments based on the evidence gathered in the research. Green represents strong deterrence, gray represents mixed deterrence, and red represents weak deterrence. Although North Korea has an interest in reunifying the Korean Peninsula, this does not appear to be a high priority or one that it believes must be accomplished in the short term. Moreover, the partners’ conventional military capability is backed up by the United States’ overwhelming nuclear superiority. Deterrence is, of course, not a static condition. Two changes could weaken the current U.S. posture: (1) a change in 1 The research and writing for this report were completed in mid-2019. Events and developments since that time are not captured in this narrative. However, although some facts may have changed or new circumstances devel- oped,