South Korea plunged into a major political crisis following its now removed president Yoon Suk Yeol’s anachronistic declaration of martial law on 3 December 2024. Although the law was quickly reversed, it caused damage to South Korea’s image as a leading liberal democracy. Questions have since been raised about Seoul’s reliability in the context of its trilateral alliance with the US and Japan. The event’s possible implications for South Korea’s foreign policy towards its East Asian neighbours are equally significant. Overall, these implications, whether international or regional, are best assessed through the lens of South Korea’s alliance with the US, as its East Asia policy also draws meaning and purpose from it.

The Yoon administration sought to strengthen the alliance with Washington, such as by signing the Special Measures Agreement for 2026-2030 (SMA) in November 2024 and The Washington Declaration on extended deterrence. The primary purpose of the SMA is to protect bilateral defence cooperation from shocks, particularly deriving from questions of burden-sharing that came up during the previous Trump administration. Further, while the South Korean Army and US military personnel stationed in South Korea are under a unified command, the two militaries are to be under the command of a US General in wartime.

Despite such close interoperability, Yoon failed to inform the US in advance about deploying the South Korean Army to impose martial law, which would have put the alliance under great stress. This could in fact have been catastrophic had North Korea decided to attack South Korea while martial law was in place. American critics of the alliance in the US could also in turn use this as evidence to support their arguments about South Korea’s unreliability. President Trump, himself an alliance skeptic, could try to renegotiate the terms of the SMA and re-emphasise the need for greater military burden-sharing. 

South Korea’s export-based economy could also suffer a setback from Trump’s decision to impose higher tariffs on US allies to curb US trade deficits. Such tariffs could reportedly lead to a US$ 44.8 billion decline in South Korea’s exports, resulting in a 0.67 per cent contraction in its GDP in the near future. Koreans are apprehensive of Trump taking advantage of domestic political disarray in Seoul to extract substantial trade and defence concessions from their country.

Political tensions in South Korea could also adversely affect historically acrimonious Seoul-Tokyo relations. The Yoon administration’s signing of the August 2023 Camp David Agreement with Tokyo and Washington was harshly criticised by the opposition Democratic Party (DP) as ‘pro-Japanese’. If DP Party leader Lee Jae-myung, who is considered a favourite for the next presidential election, comes to power as predicted, his anti-Japan stance could derail this recent rapprochement. Friction over the interpretation and documentation of the experiences of Korean forced labour at Japan’s Sado Island mines could lead to further deterioration.

North Korea is the most dominant strategic concern in the Seoul-Washington relationship. Military tensions across the Korean Peninsula have heightened since 2021. Washington retaliated to North Korea’s frequent missile tests by agreeing to deploy nuclear-armed submarines to South Korea every now and then, and expanding the scope and scale of trilateral military exercises with South Korea and Japan. Although the US and South Korea have made several lucrative assurances to North Korea in exchange for denuclearisation, these have largely been ignored by North Korea. Trump, during his last presidency, emphasised diplomatic bargaining with North Korea and cancelled military exercises with South Korea. South Koreans are apprehensive that in the absence of strong leadership in Seoul, Trump could renew rapprochement with Pyongyang—even without Seoul’s consent.

South Korea’s relationship with China, its largest trading partner, could be another major concern. Bilateral relations took a dip recently, with Beijing criticising Seoul’s expanding military posture and its security ties with Tokyo and Washington. That said, Beijing’s stance might soften or shift if the largely pro-China DP wins the next presidential election in South Korea. Growing North Korea-Russia ties could also propel China to forge stronger ties with South Korea. South Korea’s rapprochement with China however could face a major challenge irrespective of which party wins the election due to growing anti-China sentiment within the South Koreans public over issues like historical distortion, closer Beijing-Pyongyang ties, etc. With this in the background, South Korea will find itself in tight spot if Trump tries to draw it into US’ China containment strategy.

It would be wise for the next South Korean administration to attempt more autonomous diplomacy in East Asia while maintaining strong cooperative ties with the US and Japan. Seoul’s first challenge, however, will be to convince Washington and Toyo about its own reliability as an ally as well as its commitment to democracy. Dealing with a more aggressive North Korea and balancing competing Chinese and American interests will be the other two major challenges in shaping South Korea’s future foreign policy vis-à-vis East Asia. 

Dr. Pranamita Baruah Talukdar is a former Research Analyst with the Manohar Parikkar Institute for Defense Studies and Analyses’ (MP-IDSA) East Asia Center.