Resumption of Trilateral ROK-U.S.-Japan Military Exercises and North Korea Deterrence Posture: Background Analysis and Outlook for a U.S.-North Korea Summit

Executive Summary

Although President Trump ordered the scaling down of the Ulchi Freedom Shield (UFS) exercise through a personal channel, the trilateral Freedom Edge exercise, based on the Camp David agreements, will proceed in September as scheduled. These two tracks have different legal foundations and operating bodies, creating a structure where the president's political signals cannot constrain trilateral cooperation. North Korea has framed ROK-U.S.-Japan cooperation as a "trinitarian threat" and is sending separate messages to Japan and the United States, a bifurcated pattern likely to persist in future negotiations. The probability of a U.S.-North Korea summit remains limited, with the most likely base scenario (55% probability) being that exercises become entrenched while dialogue stalls. The South Korean government should explicitly separate the Ministry of National Defense and Joint Chiefs of Staff track, which maintains the exercises, from the Blue House and Ministry of Foreign Affairs track, which manages dialogue channels, to minimize political confusion.

I. Situational Analysis

Resumption of Trilateral ROK-U.S.-Japan Military Exercises and North Korea Deterrence Posture: Background and Implications for a Future U.S.-North Korea Summit

1. Background and Developments

The Ulchi Freedom Shield (UFS) exercise was originally scheduled to run for 11 days, from August 17 to 27. On August 16, the day before it was set to begin, President Trump publicly announced on Truth Social that he had instructed Secretary of Defense Hegseth to scale down the exercise [2][8]. He cited three reasons: his "very good relationship" with Kim Jong Un, the burden of defense costs, and a lack of cooperation on the Iran issue [1][6][7].

Subsequently, South Korea and the United States shortened the exercise period to five days[11]. The Ssangyong exercise was canceled altogether[13][17]. However, the cancellation of the Ssangyong exercise was different in nature from Trump's social media announcement. The actual reason was constraints on U.S. Marine Corps forces due to the potential for war with Iran, a matter that had already been communicated through working-level channels around June[8][17]. In contrast, the scaling back of UFS was a political signal sent through the president's personal channels, bypassing the Department of Defense's policy apparatus[8].

Amid these developments, North Korea escalated its rhetoric. It launched ballistic missiles on two occasions, August 6 and 12, while concurrently issuing a commentary defining U.S.-Japan-ROK cooperation as a "'trinitarian' threat that has become entrenched as a new security crisis" [12]. The Korean Central News Agency (KCNA) identified UFS as "the most direct and blatant threat," claiming the exercise was once again reaching "the 'critical point' of war breaking out" [16].

2. Current Situation

Against this backdrop, South Korea's Joint Chiefs of Staff (JCS) announced on August 28 a plan to conduct a trilateral ROK-U.S.-Japan exercise. The announcement stated that the Freedom Edge exercise would take place from September 7 to 11 in international waters southeast of Jeju Island [4][9]. The Nikkei assessed this as "an example showing that trilateral defense cooperation is continuing despite President Trump's move to scale down exercises" [1].

The timing of this announcement coincided with Chinese Foreign Minister Wang Yi's visit to South Korea. Wang was in Seoul on August 19-20 to discuss regional security issues, including the situation on the Korean Peninsula [11]. This meant that signals of deterrence against North Korea and diplomatic channels with China were activated simultaneously.

North Korea has not yet issued a separate commentary on the Freedom Edge exercise itself. However, its existing "trinitarian threat" framing is highly likely to be applied to this exercise as well [12]. North Korea's messaging channels are bifurcated. Statements in the name of Kim Yo Jong target Japan, while those from the Military Affairs Commentary Institute target the United States, Japan, and South Korea, each aimed at a different audience [12]. This suggests that North Korea's separate approaches toward Japan and the United States are likely to continue in future negotiations.

3. Key Actors and Positions

The South Korean government faces a dual challenge. It is in the contradictory position of accepting the U.S. signal to scale down ROK-U.S. exercises while proceeding with exercises within the trilateral ROK-U.S.-Japan framework. The People Power Party had previously criticized the UFS scale-down, stating that the U.S. had "thoroughly bypassed South Korea" [5]. The announcement of the trilateral exercise helps to partially offset this political burden. This can be read as a move by the government to manage concerns about cracks in the ROK-U.S. alliance while simultaneously securing a separate track for strengthening cooperation with Japan.

Within the United States, the gap between Trump's announcements via personal channels and the Pentagon's working-level channels continues to be a point of discussion. The Council on Foreign Relations (CFR) assessed that "military commanders in the United States, Japan, and South Korea have all concluded that the three countries' combined military power and readiness will be a decisive factor going forward" [6]. This shows that, separate from Trump's political signals, the institutional inertia of trilateral cooperation is being maintained at the military working level. It means that the fundamental structure, in which over 80,000 forward-deployed U.S. troops regularly conduct combined operations with South Korean and Japanese forces, will not change easily [6].

Japan appears to view this trilateral exercise as an extension of its efforts to expand defense cooperation. The tone of reporting in The Nikkei has emphasized that U.S.-Japan and ROK-U.S.-Japan defense cooperation remains unshaken despite the Trump-initiated exercise scale-down [1]. For Japan, greater uncertainty in the ROK-U.S. channel creates an incentive to affirm its own role and presence within the trilateral framework.

North Korea is pursuing a strategy of defining the trilateral exercises not as an isolated issue but as a structural threat. The very phrase "trinitarian threat" reveals its intent to frame ROK-U.S.-Japan cooperation as a single, integrated hostile force [12]. At the same time, it is not responding separately to conciliatory signals from the U.S., such as the scaling down of UFS or the cancellation of the Ssangyong exercise. This suggests that its dual strategy of handling the U.S. channel separately from the channels with South Korea and Japan is likely to be maintained during this trilateral exercise period.

China has not publicly raised its voice regarding the announcement of the trilateral exercise. Even during the earlier UFS scale-down, the Chinese Foreign Ministry's comments were limited to general statements at the spokesperson level [5]. The very fact that Foreign Minister Wang Yi's visit to South Korea coincided with the exercise announcement suggests that China is prioritizing managing the situation through the China-South Korea channel and observing developments rather than actively intervening [11].

4. Key Issues

The first issue is the asymmetric structure in which the scaling down of ROK-U.S. exercises is occurring simultaneously with the expansion of trilateral ROK-U.S.-Japan exercises. Trump's personal conciliatory signals toward North Korea and the strengthening of the trilateral deterrence posture at the Pentagon and JCS level are moving in different directions. The key question is whether this gap will persist or converge toward one side.

The second issue is the level of North Korea's response. It remains to be seen whether Pyongyang will conduct a show of force in response to the Freedom Edge exercise at a level similar to its two missile launches in August. However, it is currently more likely that North Korea will continue its pattern of a bifurcated response: maintaining a hardline stance toward South Korea and Japan while leaving room for dialogue with the United States.

The third issue is the connection to the possibility of a U.S.-North Korea summit. Unlike Trump's instruction to scale down exercises, which was a signal aimed at resuming dialogue with Kim Jong Un, the resumption of trilateral ROK-U.S.-Japan exercises could function as a conflicting message. If North Korea continues to cite the trilateral exercises as evidence of the "entrenchment of threats," it could serve to reaffirm its position on denuclearization preconditions, thereby raising the threshold for resuming dialogue. Conversely, if the United States maintains its channels with North Korea separately from the trilateral exercises, there is scope for low-intensity summit discussions to continue within a framework where exercises and dialogue proceed in parallel. In either case, the trilateral exercise itself is not seen as the decisive variable for a summit's success. Rather, the outcome will likely depend on how effectively North Korea can separate its U.S. and ROK-Japan channels during negotiations.

II. In-Depth Analysis

Resumption of Trilateral ROK-U.S.-Japan Military Exercises and North Korea Deterrence Posture: An In-Depth Analysis

1. Analysis of Root Causes

The origin of this issue lies in President Trump's personal approach to North Korea. In ordering the scaling down of the UFS exercise the day before it began, Trump cited his "very good relationship" with Kim Jong Un as a reason [2][8]. This was not a decision made through policy channels; it was an announcement from the president's personal channel that bypassed the Pentagon's working-level process [8][10]. The CFR has pointed out that this method of communication creates structural risks for allies [6].

The problem is that this personal signal conflicts with the institutionalized security cooperation among the ROK, the U.S., and Japan. The military commands of the three countries already share a consensus on the deterrent effect of their combined forces. This is supported by the structure of over 80,000 forward-deployed U.S. troops conducting constant operations from bases in South Korea and Japan [6]. The core cause of the current situation is that the president's political signals and the institutional inertia of the military authorities are moving at different paces.

North Korea's response is also precisely targeting this dual structure. The KCNA defined UFS as "the most direct and blatant threat" [16]. Simultaneously, a commentary from the Military Affairs Commentary Institute redefined ROK-U.S.-Japan cooperation itself as a "'trinitarian' threat that has become entrenched as a new security crisis" [12]. In effect, North Korea was the first to point out that, despite Trump's signal of scaling down exercises, the institutional reality of ROK-U.S.-Japan cooperation remains intact.

2. Structural Context

Security Structure: Inseparable Dual Tracks

Bilateral ROK-U.S. exercises and trilateral ROK-U.S.-Japan exercises are legally and institutionally separate tracks. UFS is an annual combined exercise based on the ROK-U.S. Mutual Defense Treaty. Freedom Edge is a trilateral cooperation mechanism established after the 2023 Camp David agreements [4][9]. Trump's authority to order a scale-down is limited to the former. The latter is managed through working-level consultations among the military authorities of South Korea and Japan and the U.S. Indo-Pacific Command.

Because of this structure, political signals from the president's personal channel cannot constrain the trilateral cooperation track. This is the context for The Nikkei's assessment of the announcement as "an example showing that trilateral defense cooperation is continuing despite President Trump's move to scale down exercises" [1]. A dual structure, where political signals from Washington and working-level security cooperation proceed in parallel, has become entrenched.

Political Structure: A Mechanism to Offset Domestic Political Burdens

Within South Korea, the scaling down of UFS has already become a political issue. The People Power Party criticized it, claiming the U.S. had "thoroughly bypassed South Korea" [5]. The government thus has an incentive to offset the political burden incurred in the ROK-U.S. channel through the ROK-U.S.-Japan channel. The timing of the trilateral exercise announcement, coinciding with Chinese Foreign Minister Wang Yi's visit, can also be interpreted in this context [11]. It can be seen as a strategic move to manage domestic concerns about a security vacuum by simultaneously activating deterrence signals against North Korea and diplomatic channels with China.

Economic Structure: The Linkage between Defense Cost-Sharing and Arms Acquisitions

One of the reasons Trump cited for scaling down the exercises was the burden of defense costs [2][8]. This is likely to be raised again as part of a package with demands for contributions in the Strait of Hormuz [5][8]. North Korea's recent threat of a "strong response" to a $125 million ROK-U.S. arms deal [18] illustrates a cyclical structure where strengthening security cooperation immediately triggers a reaction in the defense industry sector. The continuation of trilateral exercises could serve to reactivate this cycle.

3. Historical Precedents and Comparison with Similar Cases

The current situation follows a trajectory similar to the pattern of exercise adjustments around the Singapore and Hanoi summits in 2018-2019. At that time, the first Trump administration also sought to create a climate for dialogue by scaling down or suspending large-scale ROK-U.S. combined exercises (such as Ulchi Freedom Guardian). However, the framework for ROK-U.S.-Japan intelligence sharing and small-scale combined exercises was maintained. There is already a precedent for conciliatory signals at the presidential level proceeding in parallel with the maintenance of a deterrence posture at the military-authority level.

The difference this time is that the rationale for the scale-down order is multifaceted. In 2018, the sole objective was to create a climate for dialogue. This time, three reasons are intertwined: the personal relationship with Kim Jong Un, the burden of defense costs, and the Iran issue [2][8][10]. The complexity of the rationale is evidence that the priority of this measure is not clear even within the Trump administration. In fact, the cancellation of the Ssangyong exercise stemmed from a practical cause—troop constraints due to the war in Iran—and had already been communicated at the working level around June, before Trump's social media announcement [8][17]. Its causal pathway is entirely different from that of the UFS scale-down.

North Korea's "trinitarian threat" framing also has precedents. In 2016-2017, during the signing of the ROK-Japan General Security of Military Information Agreement (GSOMIA), North Korea protested by defining trilateral cooperation as "the materialization of a military alliance" [12]. What is new this time, however, is the bifurcation of messaging channels, with statements targeting Japan issued in the name of Kim Yo Jong and those targeting the ROK, U.S., and Japan issued by the Military Affairs Commentary Institute [12]. This suggests that North Korea may adopt approaches of varying intensity in future negotiations with Japan and the United States.

4. Key Variables Shaping Future Developments

First is how long the gap between Trump's personal channel announcements and the Pentagon's working-level channels will last. So far, a clear gap has been observed between announcement and implementation [10]. If this gap is not closed, trilateral ROK-U.S.-Japan cooperation is likely to operate independently, regardless of Trump's political signals.

Second is the timing of the re-emergence of demands for defense cost-sharing and contributions in the Strait of Hormuz as a package deal [5][8]. If these demands become concrete, the South Korean government will have to devise a separate negotiating strategy to balance the security card of continuing trilateral exercises against the demand for a greater economic burden.

Third is the change in the level of North Korea's rhetoric. Pyongyang has not yet issued a specific commentary on the Freedom Edge exercise itself [12]. Whether its existing "trinitarian threat" framing is applied to this exercise, or whether it leads to a separate military response (such as a missile launch), will be an indicator of the next stage of tensions.

Fourth is whether China continues its wait-and-see approach following Foreign Minister Wang Yi's visit [5][11]. If Beijing moves beyond a general response to explicit opposition to the trilateral exercises, the burden on the South Korean government of managing dual channels with both China and North Korea will increase.

Depending on the combination of these four variables, the most likely path for a future U.S.-North Korea summit remains one where dialogue stalls while the exercise scale-down is maintained only formally [10]. The very fact that trilateral exercises are continuing is more likely to reinforce North Korea's existing "trinitarian threat" framing than to provide it with new incentives to negotiate.