Japan-ROK Relations After Yoon: Shaking Hands to Survive the Trump Shakeup

On April 4, 2025, the Constitutional Court of the Republic of Korea unanimously upheld the impeachment of President Yoon Suk Yeol and his removal from office. In the absence of a democratically chosen president, an election is to be held within 60 days and its winner immediately installed as South Korea’s leader.

The oft-voiced concern here is that the change in leadership will mean a giant step backward for Japan-South Korea relations. President Yoon Suk Yeol, a conservative, had promoted closer ties with Japan, taking a conciliatory stance on the historical disputes that have long soured bilateral relations, including demands for compensation of Korean laborers conscripted by Imperial Japan during World War II. By contrast, Lee Jae-myung of the Democratic Party, the top contender for the presidency, is a leftist who has taken a hard line on such issues in the past. There are fears that Japan-South Korea relations could deteriorate sharply under a left-wing government headed by Lee Jae-myung.

While these fears are not without grounds, it is important to realize that for Seoul, the historical grievances and territorial disputes that have defined diplomatic relations with Japan over the past few decades are receding in importance relative to other foreign-policy concerns. This is because of major changes in the domestic and international environment.

Polarization and Paralysis

Let us look first at the domestic situation. The first factor to take note of here is mounting ideological polarization. Public opinion in South Korea is sharply split between the conservative and liberal camps, as was evident in the large and impassioned demonstrations for and against Yoon’s impeachment. The policies of the country’s political parties have mirrored this tendency, taking on an increasingly pronounced ideological cast designed to mobilize core voters. To survive the party primaries amid this left-right polarization, candidates must position themselves at one end of the spectrum or the other, rather than the middle. As a result, the policies of the ruling and opposition parties have diverged to the point where productive dialogue is almost impossible.

Under these circumstances, the administration—whether controlled by the conservative or the liberal camp—has its work cut out getting enough of the opposition on board to push a coherent agenda through the legislature. This was a particular problem for Yoon, since the liberals held a majority in the National Assembly. Even if another conservative were to win the upcoming election, they would face similar difficulties, at least until 2028, when the next legislative elections are scheduled.

Another point to keep in mind is that, in the current political environment, South Korean politicians are unlikely to target foreign relations as a major election issue. With the presidential election less than two months away, the conservative parties have yet to unite behind a single candidate, making it impossible to discern the outlines of an electoral platform. In the liberal camp, Lee Jae-myung has been too busy attacking the administration to hammer out a set of concrete policies on the domestic issues voters care most about, let alone external affairs. In any case, Tokyo is scarcely South Korea’s top foreign-policy priority. Substantive debate on relations with Japan did not figure prominently in the last two presidential elections, and it is not likely to do so this time either.

What this means is that South Korean policies vis-a-vis Japan will be determined after the presidential race, not during it. And those policies must take into account ominous changes in the international environment.

Fallout from America First

The first matter of concern on the international front is the impact of the “America first” policies being pursued by the government of US President Donald Trump. Under the current administration, America is swiftly descending into economic protectionism and isolationism, a trend epitomized by Trump’s extreme “reciprocal tariffs.”

In the field of security, moreover, Washington has shifted from a policy of bolstering the existing international order in cooperation with like-minded countries to one of ratcheting up the pressure on friends and allies in a bid to lighten the perceived burden of those partnerships. Under Trump, in short, the US government itself is demolishing the US-led international order.

South Korea has no more important partner than the United States, its ally since 1953. By relinquishing its leadership role in international society, the United States is leaving Seoul’s foreign policy rudderless. South Korea occupies a precarious geopolitical position, with a hostile North Korea just beyond the narrow demilitarized zone and China looming across the Yellow Sea. Were the United States to reduce its regional presence dramatically, it would seriously undermine South Korea’s security.

Implications for Japan-ROK Ties

Such a withdrawal by the United States would affect Japan-South Korea relations in a number of ways.

First, it would deprive South Korea’s defense policy of direction and thereby remove the mechanism that keeps South Korea’s security policy in step with Japan’s. Until now, both countries’ defense policies have been built around the Pentagon’s regional strategy. That is why our security policies have developed in tandem despite our political differences, including those rooted in historical disputes. If the United States detaches itself from the region and stops providing security policy guidance, Japan and South Korea will be forced to fashion their own defense policies independently, and without close consultation and coordination, those policies will cease to mesh.

Second, a withdrawal by the United States would deprive our two countries of an important intermediary. Washington has repeatedly intervened to dial down Japan–South Korea tensions whenever they threatened to compromise security cooperation in the region; the rapprochement brokered by the administration of Barack Obama between Prime Minister Abe Shinzō and President Park Geun-hye (2013–17) is just one example. It seems doubtful that the Trump administration will assume the same role. This means Tokyo and Seoul will be obliged to iron out their own differences—an urgent matter both for South Korea, with its worsening internal divisions, and for Japan’s weakened Liberal Democratic government.

Another key development on the international front is the change in North Korea’s policy toward the South. Since the end of 2023, Pyongyang has officially abandoned the goal of peaceful reunification and now classifies South Korea as a hostile state. This change has had a direct impact on the foreign policy of the South Korean left, which has traditionally advocated dialogue predicated on the possibility of peaceful reunification. The option of reaching out to China, a policy initially embraced by President Park Geun-hye, is no longer realistic given the rise of anti-Chinese public sentiment since 2016, when China launched an economic offensive against South Korea in response to Seoul’s decision to deploy a US Terminal High Altitude Area Defense (THAAD) antimissile battery in South Korean territory. In this sense as well, there is much uncertainty surrounding Seoul’s foreign policy going forward.

Focusing on Common Ground

Viewed from this perspective, it seems clear that the top priority for Japan and South Korea today should be rethinking their own foreign policies and defining the role of the bilateral relationship within those strategies—not struggling to resolve one historical grievance after another. How should Japan and South Korea, individually and collectively, rebuild their security policies with America’s diminished presence in mind? It seems clear that both countries will need to expand their own defense capabilities while stepping up cooperation and coordination with one another. If that is the case, then South Korea may have to abandon its instinctive opposition to any military buildup by Japan and even accept the possibility of a revision of Japan’s war-renouncing Constitution.

Much the same applies to economic relations between our two countries. If the United States continues down the path of protectionism, Japan and South Korea must safeguard their shared interests by working together to uphold a free trade system that functions without American participation. To that end, Japan may need to adopt a more positive attitude toward the idea of South Korea’s membership in the Comprehensive and Progressive Agreement for Trans-Pacific Partnership. It may also need to consider the admission of China, which has expressed a clear interest in joining. The future of the Asia-Pacific could hinge on Japan and South Korea’s ability to display regional leadership by addressing these challenges.

What is clear in all events is that Japan and South Korea can no longer afford to let squabbles over territorial jurisdiction and historical interpretation poison the bilateral relationship. Under the circumstances, nothing could be less helpful than to pigeonhole South Korea’s government as pro- or anti-Japanese. The important thing now is to confirm both countries’ positions as responsible, independent members of the regional and international community and rebuild the bilateral relationship accordingly.

(Originally published in Japanese. Banner photo: Opponents of President Yoon Suk Yeol celebrate the South Korean Constitutional Court’s decision upholding his impeachment, Seoul, April 4, 2025. © AFP/Jiji.)