Effects of the North Korean Threat and the US Alliance on Japan-ROK Cooperation

• In Event: North Korea and Its Neighbors

Abstract

Japan and the Republic of Korea (ROK) are democracies sharing liberal democratic values and adhering to human rights. Security treaties exist between Japan and the US, as well as between the ROK and the US.
All three share a military threat from North Korea, with concerns about frequent North Korean missile tests and its nuclear program. North Korea has expanded its ballistic missile program and nuclear program under Kim Jong Un.
In 2022, North Korea conducted a record high of 99 missile tests, followed by 36 tests and the launch of a spy satellite in 2023. Two tests in the first two weeks of 2024 and an announcement to launch more satellites suggest activities showcasing military strength will continue in 2024, demonstrating a continued high-threat environment for the trilateral alliance.
In response, Japan-ROK-US security cooperation increased in 2023 with multiple joint maritime exercises, the first trilateral aerial drill, and the establishment of a trilateral mechanism to detect and assess North Korean missile launches in real-time. Trilateral security cooperation can be expected to increase further in 2024, with a multi-year exercise plan announced in a December 2023 trilateral ministerial joint press statement.
However, bilateral Japan-ROK security cooperation has remained on a much smaller scale than their cooperation with the US, despite shared democratic values and the geographical closeness of the shared threat by North Korea. Japan and the ROK do not conduct bilateral military drills or sign a security treaty comparable to the Japan-US and ROK-US treaties. Japan-South Korea joint exercises as responses to North Korean tests could only be observed as trilateral actions that included the US, e.g., in 2017, 2022, and 2023.
In addition to small-scale security cooperation, Japan-ROK political relations alternate between cooperative and tense, despite the existence of the North Korean threat, the concern over North Korean nuclear tests, and the shared alliance with the US.
The “quasi-alliance theory” suggests that common alliances, such as the Japan-US and the ROK alliance, can explain periods of increased interstate cooperation.
In contrast, the “external threat hypothesis” proposes that external threats, such as North Korean missile or nuclear tests, can offer explanations for periods of increased cooperation.
This paper tests whether the “quasi-alliance theory” or the “external threat hypothesis” can provide explanations for the development of Japan-ROK cooperation from 2015 to 2023. The analysis explores the following questions: Does the shared alliance with the US, or the North Korean threat influence Japan-ROK government cooperation? Among North Korean missile tests, nuclear tests, and US engagement towards Japan and South Korea, which factors can best explain the development of Japan-ROK cooperation from 2015 to 2023?
To answer these questions, the relationship between data for bilateral government cooperation with North Korean missile tests, nuclear tests, as well as US military personnel in Japan and the ROK will be analyzed using a vector autoregression (VAR) model.
From 2015 to 2023, Japan-ROK relations have alternated between cooperative and tense relations, making it a representative time period of the bilateral relationship. Longstanding differences over history caused relations to deteriorate during the time of analysis, with a war reparations debate from 2018 to 2021, or a dispute over the exports of semiconductor materials from 2019 to 2023. In contrast, Japan-ROK relations reached a historical high in 2015 with the signing of a governmental agreement intended to settle the war reparations debate over Korean forced prostitution in World War II. In 2022, relations have recovered to become harmonious since current South Korean President Suk Yeol Yoon assumed office, working proactively towards positive ROK-Japan relations. In 2023, Yoon met with Japanese Prime Minister Fumio Kishida after a 12-year hiatus of ROK state leader visits to Japan, resumed a “Shuttle Diplomacy” of regular political high-level exchange between Japan and the ROK, and resolved the semiconductor trade dispute. The positive turn in Japan-ROK relations was lauded by US President Joe Biden, who encouraged Japan-ROK security and political cooperation since 2021 by facilitating bilateral meetings. US engagement before Yoon’s 2023 Japan visit is shown by about 40 preparatory trilateral meetings.
To determine which factors influenced Japan-ROK cooperation from 2015 to 2023, the analysis uses a mixed-method approach of International Relations theories and quantitative methods with daily data for North Korean missile tests and nuclear tests from the Missile Defense Project at the Center for Strategic and International Studies. Data on US military personnel stationed in Japan and the ROK is downloaded from the website of the US Department of Defense, and data on Japan-ROK government cooperation from the GDELT Event Database.

Author

• Franziska Schultz, Bowling Green State University