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What the Revamp of the Japan-US Alliance Structure Means for South Korea

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What the Revamp of the Japan-US Alliance Structure Means for South Korea

New security and military arrangements will have knock-on effects for both Japan and South Korea, their respective U.S. forces, and the regional security architecture.

What the Revamp of the Japan-US Alliance Structure Means for South Korea

Fighter aircraft from the U.S., Japan, and South Korea conducted a trilateral escort flight of a U.S. B-52H Stratofortress Bomber operating in the Indo-Pacific, Oct. 22, 2023. U.S. F-16s from the 80th Fighter Squadron, 8th Fighter Wing flew alongside Japan Air Self-Defense Force (JASDF) F-2s from the 8th Air Wing, and Republic of Korea Air Force (ROKAF) F-15Ks from the 11th Wing.

Credit: U.S. Air Force photo by Senior Airman Karrla Parra

Not many realize that the United States had a Far East Command (FECOM) in the 1950s due to the Korean War and its ramifications. The gigantic battle command was then split into two subunified U.S. Commands in both South Korea and Japan, in the form of the United States Forces-Korea (USFK) and the United States Forces-Japan (USFJ). Each carries out their respective roles as parts of the U.S. “hub and spokes” alliance system.

The USFK, composed of approximately 30,000 servicemembers and ground-combat related assets, serves not only to protect the Korean Peninsula from possible North Korean attacks, but also to maintain stability in Northeast Asia as the first responder to any ground conflicts. The USFK has its own autonomous operational control (OPCON), and the commander of the USFK is a triple-hatted four-star general, simultaneously assuming the roles of the commander of the United Nations Command and the commander of the Korea-U.S. Combined Forces Command (CFC-K).

The story is a little different for the USFJ. Currently led by a three-star U.S. general, the USFJ, despite its 55,000 servicemembers and rich aerial and naval assets, has functioned as a “policy headquarter,” answering both bureaucratic and combat orders from the Indo-Pacific Command (INDOPACOM), without any autonomous OPCON. 

However, Japanese Prime Minister Kishida Fumio’s state visit to the United States in April is certain to cause new challenges for the U.S. hub and spokes alliance system assisted by the two subunified U.S. Commands. Priorities between the two “spokes,” South Korea and Japan, might overlap and in some cases conflict, necessitating adroit handling by the U.S. government. 

Kishida’s visit had three aims: to ensure Japan’s new status as a “global” security partner, enhance the United States Forces-Japan’s class and eminence by improving the two nations’ combined Command and Control (C2) abilities against China, and bring in a U.S. four-star general to head the USFJ. The current three-star USFJ commander has not wielded the same influence as the USFK commander, who, if necessary, can even request a meeting with the Korean president. Moreover, the USFK commander can operationally control United Nation-led troops in case of another Korean War, and lead both Korean and U.S. troops under the CFC-K. It is no surprise that the USFK commander is regarded as an integral member of the senior U.S. military leadership. 

So why the upgrade to the USFJ commander? 

Against the backdrop of possible (even probable) Chinese assertiveness in the region, the U.S. government expects the USFJ to serve as a nimble aerial and naval power projection entity, while the USFK is hamstrung by 1.2 million North Korean soldiers just 30 miles away from Seoul. By equalizing the capacity and capabilities of both commands, U.S. Forces will have streamlined access to different regional combat assets – currently separated, generally speaking, between ground troops and guns in South Korea (along with some aerial and naval assets, of course) and strong aerial and naval assets in Japan – to create room for flexible, agile joint and combined operations, as the volatile situation demands. Assigning a four-star general would lay the groundwork for the USFJ to assume not only an independent OPCON to shorten the crisis response time by not having to wait for the INDOPACOM, but also smooth the asset transfer between two same-ranked U.S. commanders. 

However, it is vital to remember this new, fluid strategy conflicts with the already-orchestrated Korea-U.S. CFC-K structure. Encompassing both the USFK and the Korean Armed Forces, the CFC-K operates based on the orders of the Korean and U.S. presidents, the commanders-in-chief, as well as on the established agreements of the Pentagon and its Korean counterpart. This allows the execution of the defense of Korea via seamless, patterned operation plan against possible North Korean invasion scenarios. While the U.S. and Japan still need to hash out the exact ramifications of Kishida’s aims, adding the USFJ to the established defense equation of South Korea would require relevant stakeholders’ immediate attention and deliberations. Subtleties can be costly in situations requiring split-second decisions.

The current USFK-USFJ relations, chain of command, and operation plans do not reflect a scenario of two four-star generals with independent OPCONs, possibly sharing limited U.S. assets in the region. That might seem arbitrary, even previously unthinkable, from South Korea’s standpoint, since U.S. assets in Korea have always been considered immovable. Moreover, under the new set-up, any such transfer would be decided based on consultations between the USFJ commander and the USFK commander, not orders from the INDOPACOM or the CFC-K as it stands now. 

For instance, an aerial and naval reinforcement request from the USFK to the USFJ to defend the Korean Peninsula might not be met promptly if the USFJ commander’s combat priority is defending a besieged Taiwan, not South Korea. In this case, South Korea’s purview cannot dictate how to rotate U.S. assets, which is, lawfully, between two U.S. commanders. 

Of course, one option would be the USFK commander putting on his “CFC-K commander hat,” to assume more bureaucratic priority than the USFJ commander, but that requires trilateral consultations and formal agreements. This underscores the need for deft handling. The CFC-K commander, though the same person as the USFK commander, speaks partially for the Korean military, and in that sense the issue of asset and personnel transfers is no longer confined within the U.S. Forces, but involving three governments: South Korea, the United States, and Japan. Naturally too, Japan and the USFJ would also want a clear blueprint of when the CFC-K commander’s orders would assume more priority over the USFJ commander’s. 

Also, while denied at this point, the possibility of the USFJ activating a Combined Forces Command-Japan with the Japanese Self-Defense Force is yet another variable. In that case, there would be two Combined Forces commanders in the region, each considering the opinions of their respective deputy commanders, who, in turn, answer the orders of their commanders-in-chief, one in Seoul and the other Tokyo.

This multivariable equation, more than ever, necessitates the trilateral alliance to devise a clear, well-thought out, and flexible deconflict plan concerning the two battle commands, the USFK and the USFJ, while also heeding each state’s national sentiments and the vox populi. This is not an easy task, but it would be tremendously worthwhile to investigate smart ways to do so for regional peace and the normative and inclusive international order. 

This renewal of order and chain of command is only a beginning, and this South Korea-Japan case would be an invaluable precedent for future deconflict efforts involving other U.S. allies.