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Japan and South Korea, Grasping for Hope and Mutual Confidence

Relations are better between Japan and South Korea but for an enduring partnership the two must overcome historical issues and the 2018 radar lock-on dispute.



Prime Minister Kishida Fumio and President Yoon Seok-yul are talking before their Camp David meeting in August 2023. (©ROK Presidential Office)

Japan, South Korea, and the United States have been ramping up their military cooperation. In October the three countries performed their first-ever aerial drills over the Korean Peninsula. 

It included South Korean aircraft navigating above the Tsugaru Strait for the first time in 10 years. The strait's passage is very narrow and Japan has traditionally authorized this maneuver between its Honshu and Hokkaido islands exclusively for the US, its sole ally. But military cooperation in the region has become more salient in recent years after joint Chinese and Russian naval exercises sent their fleets sailing through the strait.

Yoon's Partnership Ambitions

The political context of this enhanced military coordination is even more crucial. In August 2023, leaders of the three democratic nations held a summit at the Presidential retreat in Maryland. The result was the Camp David Principles

Though not a military alliance, the Principles herald a "new era of trilateral partnership' to promote shared values in the Indo-Pacific and beyond. The August summit also reaffirmed security commitments amid rising tensions on the Korean Peninsula. Moreover, it addressed cooperation in another strait: the one separating Taiwan from communist China.

President Yoon Seok-yul, President Joe Biden, and PM Fumio Kishida (from left to right) walk together before Camp David for a trilateral summit (©ROK Presidential Office)

These developments have been attributed, in part, to South Korean President Yoon Suk-yeol's efforts to expand military partnerships since assuming office in March 2022. But Yoon's ambitions go beyond emboldening traditional alliances. He aspires to join larger security architectures such as the Quad and possibly AUKUS

Yoon's endeavors are also a sharp departure from the Moon Jae In administration, his predecessor. During his term, Moon was cool toward revitalizing ties with Tokyo and Washington. That was largely due to his apparent priority of appeasing Pyongyang and Beijing.

The thaw in Japan and South Korea's relations under Yoon's leadership is certainly welcome. Yoon and his Japanese counterpart, Prime Minister Fumio Kishida, have gone out of their way to demonstrate their goodwill and desire to improve ties. 

Roadblocks to a Deeper Partnership

Still, concerns remain. Notably, it is unclear whether the two nations' militaries have regained mutual trust to match the warming bond between their respective commanders-in-chief. 


In particular, two incidents from the Moon era translate into lingering doubts about the Asian neighbors' ability to build trust and the sustainability of their military coordination. One involves a naval incident and the other each country's defense intelligence.

First, the naval radar lock-on dispute remains unresolved nearly five years after it rocked the two country's relations. Both Tokyo and Seoul continue to hold diametrically opposing accounts of the event. 

On December 20, 2018, a South Korean Navy Aegis destroyer and two maritime coast guard vessels were rescuing a wooden North Korean boat drifting in the Sea of Japan/East Sea. A maritime patrol aircraft from Japan (Kawasaki P-1) also approached the scene. At that point, the South Korean warship directed its fire-control radar at the Japanese aircraft. That is according to Tokyo officials.

Fire-control radar is used to pinpoint the location of hostile targets for aiming missiles or other projectiles. The act of beaming the radar is considered just one step away from actually firing a weapon. 

A camera captures Japan's maritime patrol aircraft, Kawasaki P-1 flying near the scene of South Korean naval and coast guard vessels rescuing a North Korean boat. The P-1 was subsequently locked on by fire-control radar. (©YTN News/video taken by the Korean Coast Guard)

South Korean officials immediately refuted these allegations. They claimed instead that the Japanese aircraft navigated over their vessels in a hostile low-altitude pattern. South Korean military authorities claimed that the threatening flight pattern prompted the destroyer to direct optical cameras at the aircraft. But, they said, no radars were employed, other than for search purposes. 

Breaking Through the First Impasse

With both parties obstinately refusing to yield, the dialogue over the 2018 incident had been in a stalemate until June 2023. Japan's then-defense minister Yasukazu Hamada, and South Korea's then-defense minister Lee Jong-sup held a bilateral meeting. The two defense chiefs abruptly agreed to bury the hatchet over the radar-lock incident in the interest of responding to North Korea's escalating security menace. 

While this could be a positive pivot, if the past is any indication the buried hatchet may resurface. Historically, Japan and South Korea have tended to sweep contentious disputes under the rug. It is what the Japanese often call tana-age (棚上げ). Literally, it means "shelving" to divert attention to more pressing matters. 

However, wishing problems away has often backfired. This has been especially evident in historical disputes. For example, differences over the comfort women issue and the territorial feud over Takeshima Island/Dokdo Island. 

Hampering Regional Defense

The second leftover problem is Moon Jae In's unilateral decision to withdraw from GSOMIA in 2019.


GSOMIA was originally proposed by South Korea to Japan in 1989. After several failed negotiations, the two countries finally signed an agreement in November 2016 to exchange vital military intelligence. The years of haggling over the deal paid off. Following GSOMIA's inception up to around August 2019, the signatories exchanged crucial military information 29 times, including on North Korea's missile launches.

Former Senior Minister for Foreign Affairs and Ambassador to Korea Yasumasa Nagamine and Minister of Defense Han Min-goo sign the Japan-South Korea GSOMIA agreement at Seoul in 2016 (©Ministry of Foreign Affairs Japan)

But in 2019, Moon, over the United States' objection, decided to terminate the agreement. (The decision was later suspended.) He said it was in protest of Tokyo's having removed South Korea from its white list of preferred trade partners. 

Self-Defeating Behavior

That sudden move, also tied to Japan-South Korea disputes over wartime history, set a dangerous precedent. Scott Snyder, senior fellow for Korea Studies at the Council on Foreign Relations, even called Moon's decision "self-defeating." The memory of the GSOMIA incident underscores that military partnerships are contingent, subject to change–even abrogation–when a new leader takes office.

While President Yoon has agreed to normalize the GSOMIA agreement, skepticism towards Seoul hasn't completely dissipated. Concerns still loom large about fluctuations in South Korean politics. Should Yoon's party face a major defeat in the 2024 general election, or a liberal president replace Yoon when his five-year term expires in 2027, any positive changes could perish overnight. 

It also doesn't help that Lee Jae Myung, the current head of the Democratic Party of Korea and plausible presidential candidate in 2027, has referred to GSOMIA as a "treacherous agreement." It is difficult to build trust and share sensitive military secrets when at least one party to the arrangement may turn hostile to the deal whenever political winds shift.

Improving Bilateral Relations

These two contentious dilemmas from the Moon years, however, should not damage the burgeoning Japan-ROK relationship. Japan and South Korea have both been vital pillars of peace, balance, and prosperity in the Indo-Pacific for decades. When the two countries work hand in hand, Asia, and the rest of the world, are better off.

At the same time, the bilateral ties of the two Asian neighbors have always fluctuated unpredictably. Regional destabilization, due mostly to domestic political situations, has often been the result. 

Despite the presence of a common ally in the United States, and common security threats from Russia, China, and North Korea, bilateral relations between Japan and South Korea have been consistently tinged with discord.

Central to the disharmony –at least in the realm of the military– has often been mistrust. Although Kishida and Yoon are working faithfully to reinstate confidence, repairing military trust is an extremely painstaking task. Even for countries sharing common values and goals. It requires, above all else, candid dialog and unwavering commitment. 


Japan and South Korea must realize that as the military partnership heightens, so do the responsibilities and stakes. This is especially true in multinational security pacts such as the Quad and AUKUS, the latter of which two countries may one day be part of. Whether Kishida and Yoon are ready to forge an unbroken, lasting bilateral trust remains to be seen.   


Author: Kenji Yoshida and Jason Morgan, PhD
Kenji Yoshida is an associate correspondent for JAPAN Forward currently based in Seoul.
Jason Morgan is an associate professor at Reitaku University in Kashiwa, Japan.

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