The Peninsula

Seoul’s Dilemma in the Face of a New Sole Pacing Threat and Scenario

While most Korea watchers’ attention is centered on the Constitutional Court’s pending judgment on President Yoon Suk Yeol’s impeachment this Friday, concern is rising in Seoul that fundamental changes in the role of United States Forces Korea (USFK) may be underway. These changes will spark growing demands on South Korea to lean more concertedly into the U.S. strategy toward China and raise fundamental questions about the purpose of the U.S.-ROK alliance.

During U.S. Secretary of Defense Pete Hegseth’s first trip to the Indo-Pacific region—the itinerary for which did not include a stop in South Korea, likely because of the ongoing vacuum in its political and defense leadership—The Washington Post reported that Hegseth had signed and distributed an “Interim National Defense Guidance” throughout the Pentagon in mid-March. The interim guidance shifts U.S. attention to the Indo-Pacific and away from Europe and the Middle East, reportedly stating: “China is the Department’s sole pacing threat, and denial of a Chinese fait accompli seizure of Taiwan — while simultaneously defending the U.S. homeland is the Department’s sole pacing scenario.”

For alliance watchers, these potential changes—previously foreseen—should not come as a surprise. However, it appears they may finally be arriving. Consequently, speculation has grown that USFK’s 28,500 troops may be not only reduced but also recalibrated for greater strategic flexibility—commonly understood as the deployment of U.S. forces stationed on the Korean Peninsula to regional contingencies outside the Korean Theater of Operations (KTO)—in the event of a conflict over Taiwan.

These developments highlight the salience of KEI’s recently released report, Siloed No More: The U.S.-ROK Alliance and a Taiwan Conflict. Below are two sections from the report that highlight the issue of USFK’s strategic flexibility and its potential reconceptualization in the fast-changing geopolitical environment. The report is based on forty-two interviews conducted from June 2024 to February 2025 in both Washington and Seoul, with U.S. and South Korean current and former government officials, think tank experts, and academics—as well as open-source research.

Applying the Strategic Flexibility of USFK to Taiwan

The strategic flexibility of USFK is a longstanding topic of discussion and concern among South Korean experts. The topic frequently arises in commentary on the connection between the U.S.-ROK alliance and a Taiwan conflict. Relatedly, many cite the 2006 U.S.-South Korea joint statement on USFK’s strategic flexibility, which is often mistakenly referred to as an agreement.

However, based upon a close reading of the 2006 statement—and the contested nature of internal discussions that preceded it—U.S. and South Korean officials essentially agreed to disagree on the issue. They created a diplomatic framework that artfully papered over very real differences, which have not been revisited since. Indeed, in the years following the so-called 2006 understanding, U.S. defense officials reframed the concept, stressing “globally available U.S. forces and capabilities that are strategically flexible to deploy to augment the combined defense in case of crisis” (italics added) rather than their deployment away from the peninsula. The reframing aimed to reassure South Korea, an effort that continued throughout the 2010s amidst the U.S. pivot to Asia and increased North Korean provocations.

Open discussion of and commentary on USFK’s strategic flexibility for a potential Taiwan conflict reemerged in the late 2010s and early 2020s, igniting both abandonment and entrapment fears within South Korean body politic—much as it had in the mid-2000s. One U.S. respondent said discussions about USFK units not being tied to the Korean Peninsula have become more common, and internal U.S. conversations often assume USFK assets or units will be a part of a Taiwan contingency. Another U.S. respondent noted that when folks at DOD—although not necessarily at USFK—see a map and the location of South Korea and U.S. forces stationed there, they wonder why they cannot be included. Yet, another U.S. respondent with close knowledge of U.S. thinking said that when the United States goes to war, it tries to bring its friends and reduce the pain and damage to them while also using its entire toolbox and doing whatever it deems necessary to prevail.

Nonetheless, multiple respondents highlighted that USFK’s force structure, posture, and mission—namely, to deter aggression and, if necessary, defend South Korea to maintain stability in Northeast Asia—make it ill-suited for direct military contributions to a Taiwan contingency. To be sure, Seventh Air Force assets are sometimes included in open-source conflict scenarios, and peninsula-based aerial intelligence assets have been used around Taiwan in recent years. Yet, USFK is primarily postured to support a U.S. Army-led ground fight and provide for the reception, staging, onward movement, and integration (RSOI) of U.S. and multinational forces in the event of another Korean conflict.

In past years, maps used for TTXs involving a conflict over Taiwan did not extend to include the Korean Peninsula, according to one respondent. Another U.S. respondent asked why the assumption for Taiwan wargames is that China will strike bases in the Philippines and Australia but not South Korea. Multiple U.S. and South Korean respondents also highlighted that in the event an appreciable number of USFK personnel and assets were pulled from the peninsula for military deployment in a Taiwan conflict, the conflict itself likely would have significantly escalated in intensity and geographic scope, causing U.S. forces to take heavy loses and metastasizing U.S. and South Korean concerns well beyond the question of USFK’s strategic flexibility.

Furthermore, multiple U.S. and South Korean respondents noted that successive USFK commanders have begun to speak about planning for regional contingencies, often with reference to Taiwan, while reiterating USFK’s primary peninsular focus. As one U.S. respondent with a close understanding of the military command architecture on the Korean Peninsula said, the USFK commander could face a dilemma if a conflict breaks out in the region and would do everything they could to support that fight, short of actually deploying USFK personnel. Several other respondents cited remarks by Elbridge Colby, former deputy assistant secretary of defense for strategy and force development under the first Trump administration, in which he stated that “US forces on the peninsula…should not be held hostage to dealing with the North Korean problem because that is not the primary issue for the US,” as additional indication that USFK would increasingly be folded into broader regional planning and operations.

Given these varied insights, U.S. and South Korean respondents felt the alliance needed to have more in-depth, regular, and transparent discussions about the possible levels of USFK’s involvement in a Taiwan conflict and what role South Korea would need to play in filling any potential gaps. In line with this view, one South Korean respondent said the alliance should revise the earlier 2006 understanding of strategic flexibility to include more specific measures around USFK’s possible use beyond the peninsula.

Recalibrating USFK’s Posture and Structure

Throughout many interviews, the issue of recalibrating USFK’s structure and posture came up. If USFK’s current structure and posture are primarily oriented toward deterrence and defense in the KTO, with limited utility for a Taiwan conflict, why not adjust it to more effectively and flexibly align with both missions? Put differently, even if the alliance came to a better and more detailed agreement on USFK’s strategic flexibility, how much would it matter if USFK’s structure and posture remained ill-suited for anything beyond its peninsular mission?

Historically, U.S. administrations have explored the idea of transforming some components of USFK into mobile reserve units for flexible deployment across the region while seeking to reduce USFK and pass more burden to South Korea. They have also sought to transform the U.S. presence into a more naval- and air-centric structure to allow for greater flexibility and mobility both on and off the peninsula while maintaining sufficient logistics and support personnel to welcome additional U.S. forces in the event of a Korean conflict. For an assortment of reasons, these efforts never came to fruition. USFK has remained mostly structured around a U.S. Army-led ground mission.

In the context of the development of new concepts of operations (CONOPS) among U.S. defense strategists—which stress distribution, flexibility, interconnectivity, and multi-domain operations across U.S. defense infrastructure based in allied sovereign territory—multiple respondents considered the idea of USFK being restructured into something approaching the U.S. Army’s Multi-Domain Task Force (MDTF). Yet, the idea was challenged by other respondents for an assortment of reasons.

One U.S. respondent with close knowledge of defense matters on the peninsula not only highlighted South Korean concerns about such a shift—highlighted by consternation among some South Korean officials when an MDTF HQ was involved in military exercises on the peninsula—but also noted it would entail challenges within the U.S. military as it could spark inter-service rivalries and competition over billets on the peninsula depending on how the shift would change the existing four-star-led command structure. In terms of South Korean concerns, one respondent noted that while it might make sense from a broader strategic perspective to have more moveable forces, it was counterproductive when considering South Korea’s perception of the U.S. extended deterrence commitment. The implication was that if the United States felt USFK could not be held hostage to the North Korean threat, South Korea would need to fill that gap in fundamentally new ways (i.e., South Korean nuclear weapons).

Another South Korean respondent said a shift toward MDTF-like force presence would spark serious South Korean concerns about the U.S. commitment not only because it could mean a reduction or removal of the one remaining U.S. ground combat brigade but also because of USFK’s potentially new multi-purpose, regional role. Even if the MDTF offered solid capabilities for dealing with North Korea, they said, South Korea needs clear assurance in the form of real ground forces positioned there.

This, of course, is not a new argument. It relates to South Koreans’ psychological dependence on a U.S. force presence but also an acute sensitivity to the composition of that presence. Still, the respondent expressed distinct concern that U.S. defense planners were gradually reducing their focus on North Korea, which could lead to unavoidable changes in the U.S. presence and posture and a debate about the alliance’s overriding purpose. Despite South Korean officials insisting the USFK’s role “will remain unchanged,” this week’s events and the abovementioned trend lines clearly indicate otherwise.

 

Clint Work is a Fellow and Director of Academic Affairs at the Korea Economic Institute of America. The views expressed here are the author’s alone.

Image from UNC-CFC-USFK Flickr.

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