The future of US alliances in Northeast Asia
The future of US alliances in Northeast Asia
WRITTEN BY EMMA WHITMYER
1 April 2025
Understanding the importance that allies and partners play is more crucial than ever under President Donald Trump’s ‘America First’ administration. Although it has been less than 100 days since his inauguration, the world is already grappling with Trump’s dramatic changes to how the US positions itself on the world stage.
On 28 February, the world witnessed Trump and Vice President J.D. Vance’s public confrontation of a US ally in the Oval Office. Just days later, the White House announced that the US would be suspending crucial military aid to Ukraine. Trump’s dramatic policy changes since returning to office have sent mixed signals to US allies, and one can only imagine what other allies, both near and far, will have to face over the next few years. The clear signal for now is that should they fail to engage on the terms set by the Trump administration, their alliances with the US will look very different.
Seoul and Tokyo should begin preparing for a future in which they navigate regional challenges without a close ally who shares the same values.
The future of US alliances in Northeast Asia is set to undergo significant shifts under Trump’s second administration. Existing agreements may be renegotiated to align with his transactional approach to foreign policy, potentially altering the security and economic dynamics of the region. Japan and South Korea must prepare for the possibility of reduced US cooperation and increased pressure to shoulder more defence responsibilities. As the administration signals a willingness to reshape traditional alliances, both countries will need to navigate an uncertain landscape with strategic caution and diplomatic agility.
Trilateral relations in the year ahead
This June will mark 60 years since the normalisation of relations between South Korea and Japan, and while a great deal of progress was made under the Biden-Yoon-Kishida governments in relation to joint cooperation on security and prosperity, rapprochement is still not a guarantee. With increasing pressure from the Trump administration on trade and security spending, there are significant concerns that momentum for cooperation will slow.
At the same time, these challenges position Seoul and Tokyo with the opportunity to maintain engagement and cooperation in the face of mounting obstacles. Institutionalising the bilateral relationship will create stability and security for both countries, which is especially crucial when facing the threats posed by China, Russia, and North Korea to regional security. There is an ever-increasing need to condemn the deepening military cooperation between North Korea and Russia, especially in light of the recent deployment of troops to Russia. In preparation for what is to come and what is already happening, Seoul and Tokyo should not only continue to engage with the US, but also develop upon the progress made with each other, such as high-level consultations, and cooperation in the areas of security, technology, and the economy.
As they were during his first administration, tariffs are on track to be a hallmark of this Trump 2.0 — even against allies like South Korea and Japan. On 12 March, the US began levying 25 per cent tariffs on steel and aluminum imports, which will likely have significant impacts on Korean and Japanese businesses, especially those operating in the United States. Both countries might also face additional tariffs on the cars they export to the US, and companies are already responding in an attempt to circumnavigate this. South Korean company Hyundai recently announced that it will invest an additional USD 21 billion to expand manufacturing.
Just over two weeks after President Trump’s inauguration, Japanese Prime Minister Ishiba visited Washington to get ahead of potential tariffs and lay the groundwork for US-Japan relations under this administration. However, the visit appears to have been not as successful as hoped, as Japan has so far not been granted carve-outs from tariffs.
Meanwhile, South Korea continues to deal with political turmoil that harkens back to 2017, when then-President Park Geun Hye was impeached. Her ouster left the country with an interim leader as it navigated the opening days of the first Trump administration. During this time, the Trump administration was focused on addressing trade imbalances with Mexico and China, giving South Korea’s interim administration time to adjust to new US leadership. Ultimately however, Trump and his team put the spotlight on South Korea’s bilateral trade deals, deficit (which reached USD 23.1 billion in 2017), and security agreements. South Korea’s leaders will not be given a similar grace period this time around.
This week will see the South Korean Constitutional Court decide whether to uphold the National Assembly’s vote to impeach President Yoon Suk Yeol after his 3 December martial law declaration or reinstate him as president. If the impeachment is upheld, then a 60-day election campaign for the country’s next president will immediately follow. As Trump’s targeted tariff approach keeps South Korea on alert, the next South Korean president will have to be prepared to quickly and deftly navigate new trade policies from Washington.
When it comes to burden sharing, Trump is expected to renegotiate the Special Measure Agreement (SMA) with South Korea. The latest iteration of the five-year agreement was signed ahead of its late 2025 expiration by the Biden and Yoon administrations in October 2024, and commits Seoul to increasing its contributions towards the cost of US Forces Korea in 2026 by an additional 8.3 per cent or USD 1.19 billion. However, both Japan and South Korea are facing weakened currencies and slowing economies, and officials in both capitals could experience challenges if faced with pressure from the Trump administration to further increase defence spending.
The joint statement released after Ishiba’s February meeting with Trump reiterated Japan’s “unwavering commitment to fundamentally reinforce its own defense capabilities”. Still, Trump has consistently questioned Japan’s economic and security relationship and claimed that they make “a fortune with us economically”. Security guarantees from the United States have always been important, but shouldn’t be viewed as one-sided by Washington. Both Seoul and Tokyo should begin preparing for a future in which they navigate regional challenges without a close ally who shares the same values.
Adapting to new realities
South Korean officials and major business groups are already working hard to assure members of Congress and the administration that Korean companies are committed to bringing manufacturing back to the US and directing supply chains away from China. In mid-February, a business delegation led by Chey Tae-won, chairman of SK Group and the Korea Chamber of Commerce and Industry, visited Washington, and it is expected that other delegations will follow. By emphasising alternatives to Chinese goods and the benefits for American companies looking to operate and export abroad, these delegations can help the Trump administration realise the benefits of strengthening economic ties with Japan and South Korea.
Furthermore, it will be important for Japanese and Korean leaders to emphasise the importance of joint initiatives like the Supply Chain Early Warning System, which helps identify potential disturbances to all three markets. This pilot initiative was announced at the Camp David Summit in 2023, and proposes information exchanges to pinpoint key products and materials and set up systems to quickly exchange information about disruptions to supply chains, particularly in the area of critical minerals. Meanwhile, the United States should continue providing reassurances that it stands by its commitment to support resilient technology supply chains. Given their overlapping strategic interests and the ability to pool resources, it’s in the US, Japan, and South Korea’s interests to find ways to continue this kind of coordination.
Further engagement and cooperation with allies in Northeast Asia will provide significant value to the United States and its strategic interests over the coming years. While momentous progress has been achieved in the US-Japan-South Korea trilateral, there are many more opportunities to broaden collaboration and enhance existing cooperation. South Korea and Japan should continue to find ways to strengthen their regional security and economic prosperity, and hopefully their ally the United States, will take part.
It’s going to prove challenging for the United States to be tough on our adversaries when it is actively pushing away allies and partners. Seoul and Tokyo have an opportunity to improve upon the progress made with each other. While both governments should hope for the best in terms of continued alignment and engagement with the United States, preparations a future with less American engagement should be considered. In the event that US engagement in the trilateral is weakened, Japan and South Korea should continue meetings at the ministerial and leader levels, as well as cooperation in the areas of information sharing and on ballistic missile defence, as agreed upon at the Camp David Summit in August 2023. There will likely be many challenges ahead for the three countries, but efforts should be made to reduce points of friction and focus on progress made, especially in addressing disruptions to regional security.
DISCLAIMER: All views expressed are those of the writer and do not necessarily represent that of the 9DASHLINE.com platform.
Author biography
Emma Whitmyer is a Senior Program Officer for the Asia Society Policy Institute (ASPI) in New York. She is a part of the Security & Diplomacy pillar and works on issues relating to East Asia. Previously, she was a Junior Scholars Fellow with the South Korean Ministry of Foreign Affairs. Image credit: US Marine Corps Lance Corporal Haley Fourmet Gustavsen.