Key Takeaways:

- The U.S.–ROK alliance has been remarkably successful but is now out of step with South Korea’s transformed capabilities

- Modernizing the alliance is needed through the transfer of wartime operational control, easing U.S. restrictions on Seoul’s defense development, and a phased reduction of U.S. forces

- Such changes would create a more balanced, self-reliant partnership, strengthening both countries’ strategic interests while sustaining close cooperation

The mutual defense treaty signed between the United States and South Korea has accomplished its goals. Established in 1954 in the aftermath of the large-scale conflict on the Korean Peninsula, the bilateral alliance was intended to bolster South Korea’s defense capabilities, speed its economic development, and contain the spread of communism by integrating Seoul into what became a vast American empire.

It has been a stunning success. Peace has prevailed between North and South Korea for over 70 years, and South Korea has developed into a wealthy, technologically advanced democracy with a robust military of its own. South Korea has, thus, transformed.

Its alliance with the United States, however, remains stuck in the past. This must change. It is time for Washington and Seoul to modernize their relationship to better serve both countries’ strategic interests. This will require not just the long-delayed transfer of wartime operational control to South Korea, but also American military retrenchment that shifts responsibility for the country’s defense firmly into Seoul’s hands. These moves ultimately will strengthen, not weaken, the relationship between the two powers.

Today’s alliance between the United States and South Korea is much different than when the two nations finalized their mutual defense agreement decades ago. Over time, integration and coordination between the allies has increased, including through the formation of the Combined Forces Command (CFC) in 1978, military exercises on and around the Peninsula, and defense industrial cooperation. As South Korea’s own military capabilities improved and some U.S. forces withdrew, Seoul assumed a larger share of the responsibility for its security, including taking peacetime operational control of its military forces back from the United States in 1994 and playing a greater role in planning and preparing for the country’s self-defense.

Despite these changes, the alliance continues to institutionalize South Korea’s military dependence on its American ally. Delays in the transfer of wartime operational control to South Korea, for example, mean that if a conflict were to start, a U.S. general would lead the alliance’s CFC and the personnel assigned to it. The United States also continues to place caps on South Korea’s military capabilities as a condition of the alliance. Washington has long opposed Seoul’s pursuit of nuclear enrichment and reprocessing capabilities (sometimes referred to as nuclear latency) and only in 2021 did the United States finally lift range and payload limits on South Korea’s ballistic missile program. Finally, continued U.S. military presence in South Korea discourages Seoul from addressing the remaining capability gaps that it would need to fill to be truly self-sufficient.

The striking imbalance in the U.S.-South Korea relationship does not work in either country’s self-interest. For the United States, the sustained commitment to South Korea is increasingly an unnecessary burden on an already overstretched U.S. military force. With a clear conventional military advantage compared to its neighbor, South Korea does not need the United States to win a conventional war against North Korea. Its equipment is significantly higher quality and its soldiers, though fewer in number, much better trained. Seoul will need to build up its combat support capabilities, supplement its munitions stockpiles, and improve its missile defense systems to take full ownership of its self-defense, but these things are within reach with sustained investment. Moreover, the risk of a conventional North Korean attack on South Korea seems small. North Korea may pose a hybrid or nuclear threat, but neither is countered by the current U.S. military footprint in South Korea.

At the same time, keeping U.S. troops in South Korea limits U.S. strategic flexibility rather than augmenting it. U.S. forces based in South Korea will be of little use in a regional contingency involving China, for example. It is not clear that South Korea would allow U.S. naval and air forces to conduct offensive operations against China from its territory and Army soldiers (which make up the bulk of the U.S. presence on the Peninsula) will have little role to play in what would be largely an air and maritime war.

South Korea would also be better off if it were less dependent on the United States. Europe’s current predicament should warn all U.S. allies about the dangers of continued reliance on a United States that is rightly reassessing its global interests and commitments. Without sufficient military capabilities to defend its territory on its own, Europe has found itself unable to influence decisions that affect its own security. South Korea’s experience in trade negotiations offers another data point. Still reliant on the United States for security, Seoul has been forced to consider a less favorable deal than it might have been able to push for otherwise.

For the U.S.-South Korea alliance relationship to survive, a new paradigm is needed, one based on South Korea’s defense self-reliance and autonomy.

The shift to this new paradigm should be cooperative and phased. The first step should be the transfer of wartime operational control to South Korea. When the latest planned date for this transfer in 2015 was cancelled, the two parties shifted to a conditions-based timeline, tied to South Korea’s capabilities and North Korea’s nuclear development and missile threats. North Korea now possesses a robust nuclear weapon arsenal, but there is no reason this should prevent South Korea from leading the CFC in wartime. Even with South Korea taking the lead, U.S. commanders could still play a major role in wartime operational planning and decision-making on conventional military and nuclear issues.

Once this transfer is complete, the alliance partners should review and revise operational plans for protection of South Korea’s territory in peace and wartime. Updated plans should assign South Korean forces full responsibility for peacetime security and all major combat and combat support roles in wartime. The United States might continue to contribute logistical or intelligence functions as well as providing military assistance during a contingency on the Korean Peninsula.

The United States and South Korea should also address the issue of South Korea’s nuclear capabilities. Seoul has long had fears about the credibility of the U.S. nuclear umbrella and a reduced role for U.S. conventional forces in South Korea would further weaken their confidence in U.S. extended deterrence. The Biden administration’s Washington Declaration was intended to allay these concerns but is likely insufficient in today’s context. Currently, the main barrier to South Korea’s nuclear latency is the United States and the 123 agreement that is included as a condition of the alliance. Washington should relax these restrictions, allowing South Korea to develop its own reprocessing and enrichment capabilities—a move with high public support in South Korea. South Korea is a responsible actor and the risk from such a move would be minor. It would also offer both sides new policy options and leave South Korea more confident in its own defense.

Finally, the United States should set a five-year timeline for its military retrenchment from the Korean Peninsula, starting with ground combat brigades and their support forces and then most air assets and strategic enablers. Forces left behind would be small in number, including some logistics personnel, some fighter aircraft, and limited air defense assets. The reduction of U.S. forces on the Peninsula could occur alongside discussions about the scope of U.S.-backed security guarantees.

Even with a narrower formal commitment, the United States and South Korea could remain close strategic partners. But their bilateral engagement would be driven by mutual interests, rather than the conditions of a decades-old treaty. There would be other advantages to the new arrangement. The United States would benefit from having a stronger South Korean ally with a strong defense industrial base. It would also be able to reallocate resources currently dedicated to South Korea to other higher priorities. For its part, South Korea would have full control over its own defense policy, military spending, and capability development. And it would have the ability to engage with the United States on more equal terms, without the shadow of its military dependency looming in the background.

To be sure, implementing these changes may be difficult and will take time. But the changes are both required and wise, and there’s no better time than now—a moment of peace in Asia—to get started.