Since 2023, a series of challenges have emerged that could rupture trilateral cooperation in its current form. The changes of government in the US in January 2025, South Korea in June 2025, and Japan in October 2025 have eroded some of the political will of the Biden–Kishida–Yoon era.
President Trump’s preference for bilateralism and fixation on shifting the burden-sharing in US’s alliances make it unclear how much he values minilaterals as a tool in the US’s strategic competition with China. Trump routinely accuses allies of unfairly taking advantage of the US, does not appear to believe in collective solutions to security challenges, and seemingly prefers to deal with China and North Korea directly and in person – all of which undercut the principles behind trilateralism.
Trump’s capriciousness has eroded the first factor driving the US, Japan and South Korea closer together – namely their common perception of the threat from China and North Korea. On China, Trump has vacillated between treating the country as the US’s greatest threat across all domains of security and the economy, and seeking a grand rapprochement with Chinese president Xi Jinping by conceding US advantages and strategic resolve. The trade ‘truce’ between him and Xi, agreed in Busan, South Korea, in October 2025, temporarily delayed trade confrontations. But, while the US sought to accommodate Chinese demands in Busan, it was busy coercing other countries, like Cambodia and Malaysia, to not enter into agreements that would jeopardize US security interests, ostensibly with an eye towards China. References to China in the new US national security strategy, published in December 2025, follow a similar pattern. On North Korea, even though Trump has yet to make any policy decisions, the record of his first term as president suggests that he will prefer bilateral deals with the Kim regime over a collective approach.
The Trump administration has demanded that Japan and South Korea take on greater financial responsibility for their defence, with Washington reportedly asking Tokyo and Seoul to meet a target of 5 per cent of GDP on defence spending. Officials from the Department of Defense (recently renamed the Department of War) are pushing US allies to clarify its roles in the event of a war with China over Taiwan. The Pentagon is also considering restructuring US forces in South Korea to focus on China rather than North Korea, and drawing down troop numbers by 4,500. Tokyo is also concerned that the Pentagon may halt an agreed plan to move 4,000 US Marines from Okinawa, overturning a deal signed in 2013 after local residents opposed the US military presence on the island.
Trump’s insistence on shifting manufacturing activity back to the US will make it harder for the three countries to find common ground on matters of economic security.
On the economic front, Trump has imposed a 15 per cent tariff on all exports from Japan and South Korea to the US (with exceptions for certain sectors) – a decision that has shocked many in Tokyo in particular, which considers itself a model ally for the US, but received a basic tariff rate that is 5 percentage points higher than that imposed on the UK. Trump’s insistence on shifting manufacturing activity back to the US will also make it harder for the three countries to find common ground on matters of economic security, especially as initiatives involving friend-shoring and co-production come into question. Furthermore, a raid by US Immigration and Customs Enforcement (ICE) agents at a Hyundai factory in Georgia and the subsequent detention of more than 300 South Korean workers has enraged the South Korean population and politicians, with the reliability of US as an ally being openly questioned as a result. This raid also highlighted the contradictions between Trump’s immigration policy and his desire to bring manufacturing back to the US, as the US does not issue enough visas to allow enough workers and technicians to enter the country to set up such factories. As long as the bilateral alliances remain in flux around these issues, trilateral relations cannot deepen further.
In June 2025, South Korea elected a left-leaning politician, Lee Jae-myung, as its president. Despite having been a vocal critic of Yoon’s pro-Japan policies in opposition, Lee has since shown an inclination to continue the policy of rapprochement. Since assuming office, he has called for the strengthening of cooperation with Japan, while holding separate discussions over historical issues. Significantly, Lee’s first foreign visit as president was to Tokyo. This was the first such visit by a South Korean president since the two countries normalized relations in 1965. However, it remains to be seen if this ‘dual diplomacy’ approach persists, not least because the potential for friction has increased from the other side of the relationship.
In Japan, the resignation of Shigeru Ishiba in September 2025 led to the election of Sanae Takaichi as leader of the ruling Liberal Democratic Party (LDP) and subsequently as prime minister. Takaichi has previously been less apologetic over Japan’s colonial history in the region and, like her mentor Shinzo Abe, has visited the Yasakuni shrine, which serves as the memorial site for some of Japan’s leaders during the Second World War, who were later convicted as war criminals by an international tribunal. Although Takaichi declined to visit Yasakuni during talks over government formation, the more assertive foreign policy and nationalistic tendencies of her government risk stoking tensions with South Korea and setting back the progress made on cooperation.
The reasons for rapprochement under the leadership of Kishida and Yoon – common strategic interests, democratic values and the desire to uphold the rules-based international order – remain unchanged. However, cooperation between Japan and South Korea has always been susceptible to domestic grievances, especially in a deeply polarized South Korea. Progressive governments in Seoul have tended to focus on historical issues, while conservative governments have prioritized cooperation, causing fluctuation in relations between the two countries. For instance, in 2012, South Korea pulled out of the signing of the General Security of Military Information Agreement, an intelligence-sharing agreement with Japan, due to domestic tensions. The agreement was eventually signed in November 2016, but was terminated in 2019 before restarting again in 2023.
Progressive governments in Seoul have tended to focus on historical issues, while conservative governments have prioritized cooperation, causing fluctuation in relations between South Korea and Japan.
Even though the strategic imperative for trilateral cooperation remains the same, the extent to which any of the three countries involved will consider trilateral cooperation an essential tool for achieving these goals remains unclear.
But there are some positive signs. Despite a slow-down in institutionalization continuing into the second Trump administration, the three foreign ministers met in Munich in February, in Brussels in April and in Kuala Lumpur in July, signalling a continued desire for engagement. Meanwhile, some of the working-level mechanisms, such as the Trilateral Coordinating Secretariat managing board, the Defence Trilateral Talks (DTT), the meeting of the joint chiefs of staff and the meeting of the vice foreign ministers have also continued, while the three militaries have held trilateral exercises.
In the absence of an expansive, permanent secretariat, trilateral cooperation is in reality comprised of a bundle of such policies and meetings, held together by joint commitments and political will. The crucial question whether the momentum behind institutionalization from the Biden–Kishida–Yoon era can be sustained amid the growing uncertainties.
As middle-power democracies neighbouring a seemingly hostile superpower, Japan and South Korea have a clear strategic interest in working together to keep the US invested in the region, as they aim to prevent any unilateral coercive changes and uphold some kind of rules-based order. Ties between Japan and South Korea have historically been stronger when both countries fear abandonment by the US, especially in a harsh external security environment. The external security environment in East Asia has only worsened since Camp David, due to increased Chinese military and economic assertiveness, growing military and defence cooperation between North Korea and Russia, and the ‘no limits’ partnership between China and Russia. To underline the gravity of the situation, the 2025 edition of Japan’s annual defence white paper refers to it as the ‘greatest trial since the end of World War II’.
There are signs that leaders in Tokyo and Seoul grasp this strategic imperative. During a bilateral summit in August 2025, President Lee and Prime Minister Ishiba promised a ‘future-oriented’ partnership and pledged to put aside historical grievances. Prime Minister Takaichi has kept up the momentum so far, seeking to strengthen ties with South Korea in a meeting with Lee on the sidelines of the Asia-Pacific Economic Cooperation summit in October 2025. Both leaders have so far sidestepped discussing historical issues, in favour of a pragmatic bilateral relationship.
General domestic opinion in both countries is shifting, with more voters expressing positive attitudes towards cooperation. This development owes much to generational shifts, increased people-to-people ties between the two countries and growing negative attitudes towards China in both countries. Recent public polling suggests that 52 per cent of Japanese respondents felt that their country had a positive relationship with South Korea, compared with 50 per cent in 2024. More significantly, 54 per cent of South Koreans felt the same about relations with Japan in 2025, compared with just 42 per cent in 2024. For the first time since 1995, more than half of South Koreans believed that relations were in a good state. Even though considerable gaps in outlook towards historical issues remain, there is a willingness among voters in both countries to find common ground.
