Imagining a New US-South Korean Security Architecture

Declaring an official end to the Korean War should not be seen as a slippery slope to the withdrawal of the 28,500 US troops in South Korea or the end of the US-ROK alliance, although it would generate pressure to reduce the American military footprint on the peninsula and shift more of the collective defense burden to the South. There are alternative security and military arrangements the US and South Korea can and should put in place if North Korea ceases to be a military threat and an enduring North-South reconciliation takes hold on the peninsula. These changes are feasible and affordable and would maintain stability and the balance of power in Northeast Asia.

A Slippery Slope?

US opposition to an end of war declaration on the Korean peninsula has become a major impediment to progress on North Korean denuclearization. One reason for this stance is tactical: the Trump administration believes that the North’s desire for such a declaration gives it leverage to press Pyongyang for significant and immediate steps toward denuclearization, in particular, a comprehensive declaration of the location of its nuclear weapons and production sites. The other reason is strategic, as many in the US national security establishment believe that a formal end of the Korean War would deprive the United States of its longstanding rationale for the US-ROK alliance and the presence of US troops in South Korea: maintaining deterrence of North Korean aggression and a military and geopolitical counterweight to China’s rising power (often cloaked in the rhetoric of preserving regional stability).

Linking the timing of a peace declaration to North Korean moves on denuclearization may or may not prove to have tactical value. But fears that ending the formal state of hostilities will automatically lead to US military disengagement from Northeast Asia and the end of the American military footprint on the Korean peninsula are misplaced. Granted, sooner or later, if peace and security become the “new normal” on the peninsula and the two Koreas continue down the path of reconciliation, pressure could grow for reductions in and possibly the complete withdrawal of the 28,500 US troops in South Korea. Indeed, President Trump has already questioned the need for maintaining US troops in Korea and the US-ROK alliance.

Negotiations with North Korea on confidence building measures (CBMs) and conventional force reductions might also ultimately affect the US military posture on the peninsula. This presence has provided a guarantee of deterrence, security and stability in the face of North Korean hostility. But what if North Korea ceases to pose a threat to South Korea and US forces are drawn down or withdrawn completely from the South? Are there alternative defense and security arrangements that could help preserve peace and security in the region and deter Chinese adventurism?

Alliances Adapt or They Die

As history has repeatedly demonstrated, alliances that refuse to respond to changing geopolitical conditions or adapt too slowly are at serious risk of collapse. Some, like the Southeast Asia Treaty Organization (SEATO) and the Central Treaty Organization (CENTO) established in the 1950s, collapse because they either outlived their utility or were unable to fulfill the purposes for which they were intended; other alliances modernize their roles and missions, membership, and internal structures and processes in an effort to maintain their value and relevance.

Over the years, the North Atlantic Treaty Organization (NATO) has adapted its strategic concept, force posture and plans, and internal procedures—though often with great difficulty—to its changing security environment and strategic priorities. The US-Japan Mutual Security Treaty is far more balanced and reciprocal in its obligations today than it was 40 years ago. There are far fewer US troops stationed on NATO territory and in Japan today than there were during the height of the Cold War. The US-ROK alliance, codified in the October 1953 Mutual Defense Treaty (MDT), is one of the US’ more successful alliances, but it, too, has not remained static. In addition to its core mission of deterring North Korean aggression against the South, US and South Korean forces have broadened their security cooperation to include Iraq and Afghanistan. Changes have been made over the years to annual US-ROK military exercises. US force levels in South Korea have gone up and down depending on the geopolitical environment, both in and outside of Northeast Asia. In 1991, the first Bush administration redeployed several thousand US combat troops from the South along with the removal of all nuclear weapons based on ROK territory. Several thousand American soldiers from the 2nd Infantry Division were relocated from South Korea to Iraq in 2004, a change in force structure that occurred less than a year after Defense Secretary Donald Rumsfeld stated that Seoul no longer required the US military to deter a North Korean invasion.

Operational control (OPCON) of South Korean forces has also evolved. For two decades after the Korean War, the OPCON of almost all US and ROK forces in situations of war and peace was retained by the UN Command, which was commanded by a US general. In 1978, the Combined Forces Command (CFC), which was also led by a US general, assumed both armistice and wartime OPCON of US and ROK forces. Yet as ROK military capabilities improved, OPCON of South Korean forces during the Korean War Armistice was transferred from CFC to the South Korean joint chiefs of staff in 1994. There will soon come a time when a ROK-led military command is given full OPCON, an objective Defense Secretary Jim Mattis and ROK Minister of National Defense Jeong Kyeong-doo reiterated at the latest Security Consultative Committee meeting.

If the bilateral security relationship is to survive, the US and South Korea will need to engage in a difficult but necessary conversation about alliance restructuring if a peace regime on the Korean peninsula is formed. The US troop presence in South Korea, the transfer of wartime operational authority of South Korean troops from Washington to Seoul, and a review of future US-ROK security and military arrangements will all need to be on the table.

More Than One Way to Skin Security Arrangements

The US has implied a “virtual” security commitment with a number of countries, of varying depth and intensity, with whom it does not have a formal security commitment—and where the American peacetime military presence is minimal. These arrangements may be applicable in a security environment on the Korean peninsula that is evolving away from confrontation. For example, with Israel, Taiwan and many of America’s partners in the Middle East—notably Saudi Arabia, the UAE, Oman, Jordan and Egypt—political constraints preclude the construction of permanent US military bases and a large peacetime American military presence. (It should also be remembered that the US came to the defense of Kuwait in the first Gulf War even though it had no mutual defense treaty with that country.) The military and security relationships with these countries are cemented, in various degrees, by several factors including: combined exercises; the sale and logistics support of sophisticated weapons and equipment; the transfer of advanced military technologies and cooperation on military research, development and production; the pre-positioning of US military equipment; rotational US combat aircraft and naval deployments and port calls; arrangements for contingency US military access in a crisis or emergency; contingency planning, intelligence sharing and counter-terrorism cooperation; and regular, high-level military-to-military dialogue. In some countries where there is no formal US security commitment, this strategic cooperation is carried out within the diplomatic and legal framework of Defense and Economic Cooperation Agreements (DECA) and Status of Forces Agreements (SOFA) that signal a strong American commitment to joint defense.

Transitioning to Alternative US-ROK Security Arrangements

The US-ROK Mutual Defense Treaty commits the two nations to provide mutual aid if either faces external armed attack and allows the United States to station military forces in South Korea in consultation with the South Korean government. Because it memorializes the US security commitment to South Korea, there is no reason to believe that a future government in Seoul, regardless of its political or ideological persuasion, would not want to preserve the MDT in some form—as a hedge against Japan and China and the possibility, even if it becomes remote, of a return to a hostile relationship with North Korea. The MDT is a flexible instrument and is perfectly compatible with varying levels of US troop deployments on South Korean soil as well as alternative US-ROK military and security cooperation arrangements. Options would include a mix of the following approaches, none of which are mutually exclusive.

Places, Not Bases: Within United States Indo-Pacific Command (PACOM), US forces operate out of permanent bases in South Korea, Japan and Guam. But in other countries for example, Australia, the Philippines, Singapore and Thailand, a newer basing strategy, “Places, not Bases,” enables US forces to use existing facilities owned by allied and partner nations, creating a networked infrastructure from which these forces could operate in a crisis or conflict. All these facilities are configured to meet US wartime requirements for fuel, munitions storage and runway suitability. In the event a comprehensive peace and security regime on the Korean peninsula leads the government in Seoul to request a lower US military profile, the “places, not bases” model provides a viable option for accommodating South Korean preferences.

More Offshore Balancing-Lite: The US defense of South Korea relies heavily on the rapid reinforcement of the small tripwire force it maintains in peacetime with massive air, naval and ground forces from outside the peninsula. In other words, the US already practices a heavier form of offshore balancing on the Korean Peninsula. Commensurate with the decline in the North Korean military threat, the US presence in South Korea could shift even further away from highly ready, forward deployed, ground forces to a more “over the horizon” presence that would put more combat assets in Japan and Guam. Such a strategy would put greater emphasis on South Korean forces to provide more of the forward defense of its territory against North Korean aggression while the US would husband its military strength to intervene militarily if North Korea reversed course and once again became a threat to the balance of power on the Korean peninsula.

Rebalancing Military Missions: If North Korea ceases to be a threat to South Korea, any US ground and air forces remaining in Korea, along with ROK forces, could shift their focus from static territorial defense toward more regionally oriented missions and peacekeeping—a posture that would reinforce the importance the US attaches to its alliance with South Korea and the perception that this relationship remains rock solid. The operational requirements of such a peacekeeping mission would be vastly different from the “fight tonight” mantra US and ROK units have followed since the 1953 armistice was signed. As the US has done with NATO allies, peacetime combined training and operational planning with South Korean forces, as well as the composition of US forces on the peninsula, would support more expeditionary and humanitarian and disaster relief operations. This change would enable South Korea to make a greater contribution to these missions carried out by the UN, ad hoc coalitions of willing countries, or members of the ASEAN Regional Forum (ARF).

Simply put, the US force presence in South Korea should be tied to the evolving operational and geopolitical environment. If and when peace and economic and diplomatic normalization between the two Koreas is fully established, there will be a diminishing need to maintain 28,500 US troops at high levels of readiness and the current footprint of the American military’s posture in the South. The 800-pound gorilla in the room, however, is China. What role should a US presence in South Korea play in deterring the geopolitical and military threats posed by a rising China?

The Future US Security Role on the Peninsula

The more fundamental longer-term question is, if peace and security sink deep roots on the Korean landscape, what security role the US should assume not only on the Korean peninsula but also toward Northeast Asia more broadly; in other words, what is the desired end state that should be served by US forces (as well its other instruments of power)? Barring a strategic accommodation between the US and China in the region, and assuming that North-South peace is consolidated, the US could assume the role of security guarantor of the entire Korean peninsula—and the two Koreas, under this umbrella, could join America in a new triangular security partnership[1] with the purposes of: 1) preventing Chinese domination over the Korean peninsula to allow North and South Korea to determine their own futures, either separately or together; 2) managing and defusing the broader Chinese strategic threat to the Asia-Pacific region; and 3) making Japan feel comfortable with the new North Korean-South Korean entente so that it is not tempted to re-nationalize its defense posture. Although North Korea and China have mended diplomatic fences, Pyongyang perceives China’s rise as potentially threatening to its own foreign policy autonomy and political independence and might, therefore, be receptive to a closer geopolitical alignment with the US and South Korea.

With the MDT remaining in place, new US-ROK actions to demonstrate their shared commitment to Korean security, permanent peace and security arrangements for the peninsula, a new triangular US-ROK-DPRK security partnership, normalization of US-DPRK relations and continued North Korean progress toward denuclearization, there will be less need for the CFC and the continued presence of 28,500 US troops on the peninsula. It would be prudent, however, for this transition to proceed at a deliberate pace—and only after the US and South Korea gain a high level of confidence that normalization of their relations with North Korea, the end of the North Korean threat, and the creation of a peace and security regime have become permanent. Until those conditions exist, the ROK should avoid taking premature, irreversible measures, especially those affecting the future of US ground forces in South Korea.


The sky is not going to fall on the US military presence in South Korea or the US-ROK alliance if there is a formal end to the Korean War. But if the alliance is to survive and remain healthy into the future, the mission, structures, and operational concepts of the US-ROK defense relationship will have to evolve based on changing geopolitical circumstances. In the context of progress toward downsizing North Korea’s conventional military forces and infrastructure, agreements on CBMs and conventional force reductions, normalization of North-South relations and US-DPRK relations, and construction of a peace and security regime for the peninsula, the configuration of the American force posture could be changed without undermining deterrence and stability and the balance of power in Northeast Asia. However, this outcome will prove elusive unless the MDT remains in place and the US tangibly demonstrates the capacity and credibility to deter North Korea and reassure South Korea of the US security commitment.


  1. [1]

    The authors wish to thank William R. McKinney, (Colonel, US Army, Ret.), for these concepts.

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