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As U.S. steps back, South Korea must endure with small-state diplomacy

Published: 10 Feb. 2026, 00:03

Park Tae-gyun

The author is a professor of Korean studies at the Graduate School of International Studies, Seoul National University.

The United States released its “2026 National Defense Strategy” on Jan. 23, a follow-up document that operationalizes the military aspects of the “National Security Strategy” announced on Dec. 4, 2025. To understand the new defense strategy, it is necessary to first examine the broader framework set out in the earlier document. At its core is a renewed emphasis on a return to Monroe Doctrine–style thinking.

US President Donald Trump speaks alongside Secretary of State Marco Rubio, left, and Defense Secretary Pete Hegseth, right, during a cabinet meeting in the Cabinet Room of the White House in Washington on Jan. 29. [AFP/YONHAP]

The reference to Monroeism reflects the Trump administration’s view of the world. Rather than the post-1945 role of organizing global economic institutions such as the International Monetary Fund, World Bank and United Nations, the strategy suggests a shift away from involvement in conflicts outside the Western Hemisphere and toward a narrower focus on security in the Americas.

In this context, China and Russia are not described as immediate existential threats. If global primacy is no longer essential, costly great power competition becomes less necessary. Instead, the document uses the term “rebalancing,” which recalls the 1930s, when the United States accepted regional spheres of influence while focusing on domestic economic recovery.

Cover of the National Defense Strategy (NDS) released by the Donald Trump administration on Jan. 23. [U.S. Department of War website]

At the same time, the strategy establishes the First Island Chain, stretching from Okinawa through Taiwan and the Philippines to the Strait of Malacca. This recalls the defense perimeter known as the Acheson Line in 1950, though with a crucial difference: Taiwan, once excluded, is now a central element.

Another defining feature of the 2025 strategy is its strong emphasis on economic security. This evokes memories of trade tensions under the Nixon and Reagan administrations. Unlike the sanctions-based approach of Section 301 and Super 301 in the 1980s, however, the Trump administration frames economic security as the pursuit of “balanced trade” through higher tariffs.

The policy also reflects the limits of current U.S. export competitiveness. To rebuild industrial strength, Washington has pursued technology cooperation arrangements with South Korea, Japan and Britain while encouraging allied investment in the United States and the repatriation of returns. The strategy also proposes greater use of multilateral development banks.

Within this framework, allies in Europe and Asia are asked to increase defense spending and investment. Regional priorities have shifted as well. North America and Latin America have moved to the top, followed by the Indo-Pacific, while Europe has fallen to third place. The document even describes Europe as a region experiencing economic decline and “civilizational erasure.”

Such a strategic shift is historically unusual. For most of its history, U.S. diplomacy has focused first on Europe, which has been both a cultural reference point and a central arena for conflict and cooperation. America’s rise to global leadership was inseparable from its involvement in two world wars on the European continent.

Asia’s importance had previously been defined largely by Cold War conflicts such as the Korean and Vietnam wars. Today, however, the strategic center of gravity is moving toward the Indo-Pacific, home to the world’s most dynamic markets.

Reflecting this shift, the 2026 defense strategy states that global engagement is no longer automatically an obligation or even a clear interest for the United States. It emphasizes deterrence through strength rather than active confrontation and calls for a major expansion of the domestic defense industrial base.

The approach recalls the spirit of the 1950 National Security Council document NSC-68, which advocated increased military spending to stimulate economic growth amid geopolitical rivalry. The difference is that while NSC-68 relied on domestic resources, the new strategy seeks to expand the defense industry with investment from allies, framed as a “mutually beneficial alliance.”

In threat assessments, China is described as a partner with which a “decent peace” is possible, while Russia is viewed as a manageable threat. Iran and North Korea, however, are identified as more direct risks. North Korea is characterized as a “clear and present danger” capable of nuclear attack on the U.S. mainland.

Yet the strategy does not mention denuclearization of the Korean Peninsula and states that primary responsibility for responding to North Korean threats rests with South Korea. Support for South Korea is described as “more limited” than the already “limited” support envisioned for Europe.

The National Defense Strategy (NDS) released by the Trump administration on Jan. 23 (local time) indicates that Korea should assume primary responsibility for threats posed by North Korea’s conventional forces. The photo shows Camp Humphreys, a U.S. Forces Korea base in Pyeongtaek, Gyeonggi, on Jan. 26. [YONHAP]

The document also raises the possibility of adjusting the size and role of U.S. Forces Korea, recalling early post–Cold War plans for overseas troop realignment. Analysts warn that changes in wartime operational control and alliance roles could follow.

European reactions to the strategy have been sharply critical. Observers argue that it departs from the long-standing assumption that global leadership serves U.S. interests and that it reflects a retreat from internationalism and liberal values.

For South Korea, the implications remain uncertain. Predictions of troop reductions or alliance restructuring are widespread, but the trajectory of the Trump administration’s second term is difficult to forecast. Previous attempts by U.S. presidents to withdraw or redeploy ground forces abroad have often failed.

With many possibilities open and trade tensions continuing to complicate relations, the strategic environment may become as complex as it was during earlier decades of alliance adjustment. In this context, South Korea must develop a new vision for diplomacy suited to a middle power navigating a more selective United States.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.