From the Defense of the Korean Peninsula to a Core Axis of Northeast Asian and Indo-Pacific Security1)
English translation by TigerDyne Nexus. The Korean original is authoritative.
1. Statement of the Problem
Founded on the ROK–US Mutual Defense Treaty concluded in 1953, the ROK–US alliance has functioned as a core security mechanism for maintaining peace and stability on the Korean Peninsula. During the Cold War, US Forces Korea (USFK) played a pivotal role in the defense of the Republic of Korea as a forward-deployed force deterring North Korea's military threat and the expansion of communist forces. Since the end of the Cold War, however, US defense strategy for Asia has changed along with shifts in the regional security environment, such as China's rise and military modernization and the advance of North Korea's nuclear and missile threat. While expanding cooperation with its allies, the United States has reorganized the force structure and basing system of its forces stationed overseas and strengthened their strategic flexibility.
Amid these changes, the role of USFK has expanded from a forward-deployed force for the defense of the Korean Peninsula to an operational maneuver force for Northeast Asia. This is the combined result not only of changes in US strategy toward Asia but also of Korea's growing security autonomy, structural adjustments in the ROK–US alliance, greater strategic flexibility for USFK, and the relocation and realignment of its bases. In particular, the role of USFK needs to be understood in connection with US Forces Japan (USFJ). If USFK provides ground-force-centered deterrence and operational response capabilities, USFJ, built on naval, air and Marine forces, underpins strategic power projection into the Indo-Pacific region. USFK and USFJ, with their different force structures, thus operate in a mutually complementary way and create a synergy effect for the employment of US military power in the region.
These changes show that the ROK–US alliance is evolving beyond an alliance for the defense of the Korean Peninsula against North Korea's military threat into a strategic alliance that contributes to stability and order in Northeast Asia and the Indo-Pacific region. To understand the role of the ROK–US alliance and USFK today, therefore, we must look not only at the mission of defending the Korean Peninsula but also at USFK's standing in the US Indo-Pacific strategy and its links with US forces in the region, including USFJ.
2. The Changing Role of USFK: From a 'Regional Defense Force' to an 'Operational Maneuver Force'
In a research paper titled "Changes in the Roles of US Forces Korea and US Forces Japan in the Post-Cold War Era", the author explained the changing role of USFK after the Cold War as the interaction of two factors: US defense strategy toward Asia and Korea's alliance strategy toward the United States.
First, to maintain its strategic advantage in Asia, the United States expanded military cooperation with its allies and strengthened the strategic flexibility of its forces stationed overseas. From the 1990s, US defense strategy shifted from a 'threat-based strategy' to a 'capabilities-based strategy', and from the 2000s the United States pursued the realignment of its overseas forces and the acquisition of rapid power-projection capabilities as core defense strategy. The Obama administration's 'rebalance to Asia' and the Trump administration's 'Indo-Pacific strategy' made this trend even more concrete.
Second, building on its growing national power and military build-up, Korea sought to expand its security autonomy and to take a leading role in its own defense. The return of peacetime operational control, the pursuit of wartime operational control transition and the realignment of USFK bases are major products of this Korean alliance strategy toward the United States. Korea's expanding role acted as a factor that accelerated structural adjustment of the ROK–US alliance and the transition of USFK's role.
Third, the 2006 agreement between Korea and the United States on the 'strategic flexibility of USFK' was an important turning point in the change of USFK's role. While maintaining its missions of defending the Korean Peninsula and deterring North Korea, USFK expanded its operational flexibility to deploy to areas outside the peninsula according to US military needs. The realignment of USFK bases centered on the Pyeongtaek–Osan and Daegu areas, and the rotational deployment of USFK forces that began in earnest in 2014, also supported these operating conditions.
Taken together, these changes allow us to assess that USFK has expanded its role from a regional defense force for the defense of the Korean Peninsula during the Cold War to an 'Operational Maneuver Force' that maintains the military balance in Northeast Asia and responds to crises in the region after the Cold War. This change of role, however, does not mean a weakening of USFK's essential missions of defending the Korean Peninsula and deterring North Korea. Rather, it should be understood as an expansion of its missions and operating scope so that it can respond to changes in the regional security environment while maintaining the defense posture on the peninsula.
3. The Interconnection of USFK and USFJ: Providing Flexibility and a Multiplier Effect for US Forces in the Region
In understanding USFK's strategic role, its relationship with USFJ is an important element of analysis. After the Cold War, USFK and USFJ each developed different force structures and strategic functions. USFK, built on ground-force-centered forces, supports deterrence and operational response in Northeast Asia, whereas USFJ, centered on the Seventh Fleet, III Marine Expeditionary Force and Fifth Air Force, underpins US strategic projection capability in the Indo-Pacific region. Their relationship can be summarized as follows.
| Category | USFK | USFJ |
| Core strategic function | Deterrence of North Korea and operational maneuver in Northeast Asia | Strategic maneuver in the Indo-Pacific and global power projection |
| Main force characteristics | Ground-force-centered operations | Long-range projection forces centered on the Navy, Marine Corps and Air Force |
| Main roles | Defense of the Korean Peninsula, crisis response in Northeast Asia, support for regional operations | Strategic power projection, rapid regional response, protection of sea lines of communication, checking China |
| Complementary function | Provides stability in Northeast Asia and a base for ground operations | Leads regional operations through naval, air and Marine forces |
The forces of USFK and USFJ are mutually complementary. When USFK maintains strong deterrence and an operational response posture in Northeast Asia, USFJ can extend its area of operations across the Asia-Pacific, including the Indian Ocean and the Western Pacific. Conversely, USFJ's naval and air forces and power-projection capabilities underpin the operational flexibility of the ground-force-centered USFK. Their complementarity goes beyond mere geographic proximity or the sum of troop numbers. When force structure, bases and logistics support systems, intelligence sharing, and combined exercises and training are linked, the strategic and operational flexibility and utility of USFK and USFJ can grow even greater.
To maximize the multiplier effect of USFK and USFJ forces, however, constraints must be overcome. Differences in cohesion between the ROK–US and US–Japan alliances, changes in Korea–Japan relations, differences in the two alliances' priorities regarding regional threats, and the imbalance of US force deployment in the Asia-Pacific concentrated in USFK and USFJ can constrain the interlinked employment of USFK and USFJ forces. In particular, since USFJ can deploy out of area smoothly only when stability in Northeast Asia is assured, USFK's readiness and burden are closely connected to USFJ's operations as well. In the end, USFK and USFJ need to be understood both as components of their respective alliances and as a mutually complementary force system that implements US military strategy in Northeast Asia and the Indo-Pacific region.
4. Strategic Implications of USFK's Expanding Role
The expansion of USFK's role and the deepening complementarity of USFK and USFJ present Korea with new opportunities and challenges at the same time. First, Korea must maintain a strategic balance between the defense of the Korean Peninsula and contributions to regional security. The starting point and core of the ROK–US alliance is the defense of the Korean Peninsula and deterrence of North Korea's military threat. Even if USFK's strategic flexibility expands, the stability of the defense posture on the peninsula and combined defense capabilities must be maintained without wavering. At the same time, Korea must recognize the reality that peninsular security and regional security cannot be separated from each other. The safety of sea lines of communication, missile defense, security in the cyber and space domains, and regional crisis management are directly connected to Korea's economic and security interests. Korea's contribution to regional security therefore needs to be considered not as a separate burden beyond the scope of defending the Korean Peninsula but as a strategic activity that protects Korea's national interest.
Second, a consultation framework on USFK's strategic flexibility must be developed. The possibility of USFK deploying out of area affects not only US military strategy but also Korea's security and diplomatic interests. Sufficient prior consultation and close communication between Korea and the United States are therefore important regarding the specific application of strategic flexibility. In particular, a consultation framework must be developed that can examine in advance the impact on the defense posture of the Korean Peninsula, Korea's principles of response in the event of a regional crisis, and the relationship between the combined defense mission and out-of-area missions. This is not a restriction on USFK's strategic flexibility but an institutional mechanism to raise the predictability and credibility of the alliance.
Third, the linkage between USFK and USFJ must be managed from Korea's strategic perspective. The complementarity of USFK and USFJ provides a multiplier effect for the employment of US military power, but from Korea's perspective it must be examined closely how that linkage affects the defense of the Korean Peninsula and regional crisis management. To this end, ROK–US military consultations need to assess not only USFK's missions and posture but also the impact of changes in USFJ and other US forces in the region on the defense of the Korean Peninsula. In addition, Korea–Japan security cooperation and Korea–US–Japan trilateral military cooperation should accumulate practical results starting with feasible areas of cooperation such as intelligence sharing, missile warning, maritime security and disaster response.
Fourth, the ROK military's independent and combined operational capabilities must be strengthened together. The development of the alliance presupposes an expansion of the ROK military's role and capabilities. The ROK military must strengthen its independent deterrence and defense capabilities against North Korea's nuclear and missile threat while developing the interoperability needed for combined operations with US forces and multinational cooperation. In particular, strengthening the ROK military's capabilities in command and control; intelligence, surveillance and reconnaissance; missile defense; precision strike; logistics support; and the cyber and space domains becomes the foundation for raising the operational utility of the ROK–US alliance.
5. USFK's Expanding Strategic Role and the Development of ROK–US Defense-Industrial Cooperation
The change in USFK's strategic role offers new opportunities not only for the military operating scope of the ROK–US alliance but also for defense-industrial and advanced-technology cooperation between the two countries. If ROK–US defense-industrial cooperation in the past focused mainly on introducing US-made weapon systems and technology cooperation to build up the ROK military's capabilities, it now needs to develop toward combining the two countries' industrial capacity and technology bases to meet shared military requirements. In particular, the more USFK and USFJ play mutually complementary strategic roles in Northeast Asia and the Indo-Pacific region, the more linking the two countries' logistics support systems and defense supply chains will become an important element underpinning stronger deterrence on the Korean Peninsula and the alliance's sustainment capacity.
Korea possesses a considerable industrial base and technological capability in semiconductors, batteries, shipbuilding, information and communications, artificial intelligence, space and defense manufacturing. These capabilities are directly connected to the core elements of future military power. The ROK–US alliance must expand the scope of cooperation beyond traditional weapon-system-centered cooperation to joint research and development of advanced technologies, stabilization of supply chains for key components and materials, and linking of defense data and technical standards. This is also consistent with the view that the military alliance should be developed into a strategic technology alliance that shares technological and industrial bases. Ship and aircraft maintenance, parts supply, equipment maintenance and repair, and improvement of logistics support systems can become practical areas of ROK–US cooperation. In particular, if Korea's defense-industrial and maintenance capabilities reach a level that meets US logistics support systems and related standards, this could develop beyond support to USFK into maintenance and logistics support cooperation for US forces operating in the Indo-Pacific region. Interoperability is also an important task for defense-industrial cooperation. The effectiveness of ROK–US combined operations depends not only on weapon systems but on how organically reconnaissance and surveillance, command and control, and strike systems are connected. As the strategic linkage between USFK and USFJ expands, the compatibility of communications, data and command-and-control systems between the ROK military and US forces needs to be raised, and technical integration in unmanned systems and the space, cyber and electronic warfare domains needs to be strengthened.
Ultimately, the change in USFK's strategic role does not mean only a new burden for Korea; it is also an opportunity to develop Korea's industrial and technological capabilities into a shared security asset of the alliance. Through such cooperation, Korea can establish itself as a core industrial partner of the United States that supports both the alliance's military sustainment capacity and its technological competitiveness. The competitiveness of the future ROK–US alliance depends not only on the effective employment of combined forces but also on whether the two countries together build the technology and industrial base that can continuously strengthen and sustain those forces.
6. Policy Recommendations and Korea's Strategic Choice
The change in USFK's role cannot be explained by US strategic requirements alone. It is the result of the interaction of US defense strategy toward Asia, Korea's growing security autonomy and structural change in the ROK–US alliance. The future direction of the ROK–US alliance should therefore be set from a perspective that harmonizes US strategic needs with Korea's national interest.
To this end, the combined defense posture on the Korean Peninsula must first be firmly maintained. Regardless of the expansion of USFK's strategic flexibility, guaranteeing the stability of deterrence against North Korea and of the combined defense posture is the basic premise of the ROK–US alliance.
In addition, ROK–US consultation on USFK's strategic flexibility must be institutionalized. A consultation framework needs to be developed that can examine and coordinate in advance the impact of USFK's out-of-area deployments and mission changes on Korea's security. The strategic assessment of the linkage between USFK and USFJ must also be strengthened. The impact of the force structure and operations of US forces stationed in both countries on the security of the Korean Peninsula and the region must be analyzed comprehensively, and Korea's strategic interests must be reflected in that process. Along with this, the ROK military's strategic contribution to a stronger regional security posture and its role within the alliance must be expanded. The ROK military's independent defense capabilities and combined operational capabilities must be strengthened at the same time, and its practical contributions in areas such as maritime security, missile defense, intelligence sharing and advanced-technology cooperation must be expanded. In particular, ROK–US defense-industrial and defense-technology cooperation needs to be developed into an important pillar of the alliance's development. Korea's advanced industrial capabilities should be linked to the defense sector and expanded into cooperation in joint research and development, stabilization of supply chains for key components, and logistics support and maintenance, repair and operations (MRO). Given that the importance of stable logistics support and equipment maintenance and repair for US forces in the region may grow if the strategic linkage between USFK and USFJ is strengthened, a cooperative foundation must be laid that can use the technological strength and production and maintenance capacity of Korea's defense industry to strengthen the alliance's military sustainment capacity. Such industrial and technological cooperation is significant in that it allows Korea to establish itself not merely as a buyer of US-made weapon systems but as a core industrial partner contributing to the sustainment and development of the alliance's forces. Further, it can become the foundation for developing the ROK–US alliance into a strategic cooperative relationship that shares advanced technology and defense-industrial capabilities, rather than one confined to military cooperation.
Since the end of the Cold War, USFK has expanded its role into an 'operational maneuver force' for Northeast Asia while maintaining its traditional mission of defending the Korean Peninsula. USFJ, too, has developed into a 'strategic maneuver force' for the Asia-Pacific region and formed a mutually complementary relationship with USFK. These changes are the result of combining US defense strategy toward Asia with the alliance strategies of Korea and Japan, and they are closely connected to changes in the security order of Northeast Asia and the Indo-Pacific. Going forward, the ROK–US alliance must firmly maintain its core missions of deterring North Korea's nuclear and missile threat and defending the Korean Peninsula, while developing the strategic flexibility and scope of cooperation needed to respond to changes in the regional security environment. In this process, Korea must move beyond the passive stance of simply accepting or guarding against USFK's expanding role, and be able to manage the alliance's changes proactively so that they serve Korea's security and national interest. To this end, not only military consultation frameworks but also cooperative foundations in the defense-industrial, technological and industrial fields must be developed together. Korea's strategic choice should lie not merely in responding to the change in USFK's role but in actively designing the future of the ROK–US alliance by developing Korea's military and industrial capabilities into shared assets of the alliance.