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The ROK–U.S. Alliance in a Regional Context: Challenges for Lee Jae-myung’s Pragmatic Foreign Policy1) |
| October 31, 2025 |
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Sang Hyun LeeSenior Research Fellow, Sejong Institute | shlee@sejong.org
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The ROK–U.S. alliance stands at a pivotal moment. The United States is no longer the same America that upheld a liberal, rules-based, free-trade order in which South Korea thrived for decades. The resurgence of U.S. transactionalism under the Trump administration has reshaped global diplomacy, exerting pressure not only on rivals such as China and Russia but also on allies, including South Korea, Japan, and the European Union, through tariff hikes and burden-sharing demands.
In this unsettled global environment, South Korea faces multifaceted challenges—economic, diplomatic, and strategic. The most immediate difficulties concern two interrelated issues: unfinished tariff negotiations and the modernization of the alliance itself.
The first summit between President Lee Jae-myung and President Trump in Washington (August 25, 2025) yielded limited progress. Although the two sides agreed in principle to a 15% tariff framework, President Trump signaled that new demands could arise if the U.S. trade deficit persists. The size and structure of South Korea’s USD 350 billion investment package—particularly the cash ratio and funding period—remain contentious.
Despite expectations of a breakthrough at the APEC Summit in Gyeongju, U.S. Treasury Secretary Scott Bessent stated that while a “general framework” exists, “complex details” still require resolution. President Lee confirmed this stalemate in a Bloomberg interview, acknowledging that the “mode, timing, and profit-sharing” aspects of the investment package are unresolved.
At the broader global level, the uncertainty of U.S.–China trade negotiations continues to cloud prospects for regional stability. The disputes now transcend tariffs and deficits, encompassing advanced technology, rare earth exports, and semiconductor supply chains—sectors crucial to South Korea’s economic security. -
Alliance modernization has emerged as a top priority for Seoul and Washington. The rationale is straightforward: the Indo-Pacific threat environment has evolved, and the alliance must evolve with it.
As the Trump administration’s second term begins, Washington is reassessing the size and mission of U.S. Forces Korea (USFK), currently numbering around 28,500. Reports indicate that 4,500 U.S. troops—possibly the Stryker Brigade—may be relocated elsewhere. The brigade, equipped with wheeled armored vehicles, has been central to rapid response operations since 2022.
General Xavier Brunson, USFK’s new commander, described South Korea as “a fixed aircraft carrier between Japan and China,” implying an expanded regional role for U.S. forces beyond deterring North Korea. In parallel, the United States and Japan are discussing a “One Theater” concept linking the Korean Peninsula, East China Sea, and South China Sea as a unified operational space. This approach aims to strengthen cooperation among the United States, Japan, Australia, the Philippines, and potentially South Korea to counterbalance China.
Such a reorientation, however, poses challenges for Seoul. A shift in USFK’s mission from peninsular deterrence to regional power projection against China could complicate South Korea’s strategic autonomy. Furthermore, the Trump administration’s demand for higher cost-sharing is expected to intensify.
U.S. strategists such as Elbridge Colby, a chief architect of the 2022 National Defense Strategy, advocate prioritizing the China challenge while urging allies to assume greater responsibility for their own defense. For South Korea—caught between its main security guarantor and its largest trading partner—maintaining strategic flexibility will be crucial.
Several scenarios are possible: a partial troop reduction, repurposing USFK for China contingencies, or leveraging troop levels as a bargaining tool. Victor Cha of CSIS has warned that President Trump could even threaten full withdrawal to pressure Seoul on cost-sharing or trade concessions.
These debates echo those of the Roh Moo-hyun era (2006), when Korea accepted U.S. “strategic flexibility” but retained veto power over regional deployments. Preserving that principle will be essential as the alliance adapts to new realities. -
The urgency of alliance modernization becomes clear against the backdrop of deepening China–Russia–North Korea cooperation—a revival of Cold War–style bloc politics.
North Korea’s direct involvement in Russia’s war in Ukraine represents a dramatic shift. According to Ukraine’s intelligence service, Pyongyang has supplied millions of artillery shells, short-range ballistic missiles (KN-23, KN-24, KN-25), and various munitions. In exchange, North Korea reportedly receives fuel, food, and possibly sensitive military technology related to reconnaissance satellites, nuclear-powered submarines, and drone systems.
More strikingly, North Korea has deployed an estimated 16,000 combat troops to Russia since late 2024, with roughly 4,700 casualties. This unprecedented military participation provides North Korea with battlefield experience and strengthens ties with Moscow, while creating serious security implications for Europe and the Korean Peninsula.
Equally significant is the trilateral summitry among Xi Jinping, Vladimir Putin, and Kim Jong-un in 2025. Their joint appearances in Beijing (September 3) and Pyongyang (October 10) marked the symbolic consolidation of a “Northern Triangle” opposing the U.S.-led “Southern Triangle” of Korea, Japan, and the United States. Kim Jong-un’s central role at these events underscored Pyongyang’s new geopolitical confidence—bolstered by de facto recognition of its nuclear status by its northern partners.
However, the partnership remains structurally unequal. A 2025 study by Olena Guseinova (Hankuk University of Foreign Studies) found that while North Korea provided up to USD 9.8 billion in military support—equivalent to one-third of its GDP—Russia’s compensation amounted to barely USD 1.2 billion, mostly in food and oil. Still, even an asymmetrical alliance gives Pyongyang diplomatic leverage and technological gains. -
The Lee administration’s pragmatic foreign policy seeks to navigate these structural shifts by emphasizing flexibility, balance, and national interest over ideology. Yet such pragmatism must rest on clear strategic principles to avoid being perceived as opportunism.
Seoul faces a fourfold challenge:
First, South Korea should support U.S. efforts to modernize the alliance while avoiding entrapment in anti-China containment. Second, Seoul should maintain stable relations with Beijing as an essential economic partner. Third, it must respond firmly to the emerging China–Russia–North Korea alignment. Finally, Seoul should resume inter-Korean dialogue without legitimizing Pyongyang’s nuclear status.
Balancing these imperatives requires deft diplomacy. President Lee’s approach differs from Yoon Suk-yeol’s value-based foreign policy by focusing on “principled pragmatism”—strengthening alliances while keeping dialogue channels open with all neighbors. However, the perception of neutrality can erode trust if Seoul’s principles are not clearly articulated.
In potential contingencies such as a Taiwan Strait crisis, Washington expects greater allied coordination. Yet Seoul’s primary obligation remains peace and stability on the Korean Peninsula. The United States and South Korea should use existing mechanisms—such as the Nuclear Consultative Group (NCG), the Extended Deterrence Strategy and Consultation Group (EDSCG), and the High-Level Bilateral Commission (HLBC)—to clarify roles and avoid misperceptions about wartime responsibilities.
To overcome these dilemmas, first of all, the Lee administration should take every effort to address pending issues between Seoul and Washington through follow-up consultations after Gyeongju APEC summit. The conclusion of comprehensive tariff and trade negotiations in Gyeongju is a welcome development. The two nations agreed that, of the $350 billion (approximately ₩501 trillion) investment in the US that had been a point of contention, $200 billion would be invested in a special purpose vehicle (SPV) established by the US government, while $150 billion would be allocated to the MASGA (Make American Shipbuilding Great Again) project. However, the specific investment methods and sectors still require finalization through subsequent negotiations.
Second, Seoul and Washington should institutionalize strategic consultation and nuclear coordination. Strengthening policy coordination through the NCG, EDSCG, and HLBC is essential for synchronizing extended deterrence, nuclear planning, and crisis response—particularly in light of shifting regional deterrence dynamics.
Third, Indo-Pacific countries—including the United States, China, Japan, and South Korea—should collaborate to establish a regional crisis management mechanism. The Indo-Pacific currently lacks institutional frameworks for escalation control. South Korea should spearhead the establishment of risk-reduction dialogues among regional actors—potentially including China and ASEAN partners—to prevent unintended clashes and manage crises.
Fourth, Seoul should promote a principled pragmatism after successfully hosting 2025 APEC summit. Seoul’s diplomacy should combine flexibility with clarity of purpose. Its core principles—defense of sovereignty, alliance credibility, regional stability, and open markets—should guide engagement with both Washington and Beijing.
Fifth, and finally, Lee administration should align economic and security strategies amid the unprecedented geopolitical and geoeconomic turbulence. South Korea’s participation in high-tech and supply chain cooperation with the United States (e.g., semiconductors, batteries, rare earths) should be balanced by active diversification of trade with ASEAN, India, and the EU to reduce overdependence on China.
The ROK–U.S. alliance is once again being tested by global realignments and shifting power balances. The modernization of the alliance, if managed prudently, can reinforce deterrence, autonomy, and economic security simultaneously. However, mismanagement could entangle South Korea in great-power rivalries beyond its control.
President Lee Jae-myung’s pragmatic diplomacy presents an opportunity to reposition South Korea as both a reliable ally and an independent stabilizing power in the region. Success will depend on consistency—anchoring flexibility in principle, balancing economic interdependence with strategic clarity, and articulating a long-term vision for Korea’s role in a fragmented Indo-Pacific order.
| The ROK–U.S. Alliance Under Strain
1) The earlier version was virtually presented at ROK-US Alliance Trans-Atlantic-Pacific Security Forum, co-hosted by Atlantic Council and Korea Foundation, October 21, 2025.
| Modernizing the Alliance: A Strategic Imperative
| The Indo-Pacific Security Context: A Resurgent Northern Axis
| The Dilemma of Lee Jae-myung’s Pragmatic Diplomacy
※ The contents published on 'Sejong Focus' are personal opinions of the author and do not represent the official views of Sejong Institue
