Challenges to the Stability of the U.S.-ROK Alliance in Uncertain Times

Security is like air—it is often unnoticed when present, but its absence brings immediate crisis. The alliance between the United States and the Republic of Korea (ROK) plays a similarly vital yet often unacknowledged role in the ROK’s domestic political landscape. In an unpredictable geopolitical environment, the U.S. military presence in South Korea serves as an anchor of stability. It plays a crucial role in deterring North Korean provocations and preventing worst-case scenarios. However, unexpected developments in North Korea or the Taiwan Strait could pose significant challenges. In such moments, people will recognize the true value of the alliance—much like the sudden realization of the importance of air when it disappears.

The Stability of the U.S.-ROK Alliance

Despite political turmoil in South Korea, the U.S.-ROK alliance has remained stable and effective in deterring North Korea’s opportunistic provocations. When President Yoon Suk Yeol declared martial law—only to have it overturned by the National Assembly within hours—the U.S. Department of Defense promptly reaffirmed its ironclad commitment to South Korea’s defense. General Paul LaCamera, the commander of U.S. Forces Korea (USFK), also made clear that joint military exercises and operations would not be disrupted by external factors.

These statements were not mere rhetoric. During January 14–16, U.S. and South Korean forces conducted combined firepower exercises, followed by joint air force drills from January 21 to January 24. According to the ROK Ministry of National Defense, 113 combined exercises and trainings are planned for the first half of 2025—a notable 10% increase from the same period in 2024.

To better understand the alliance’s stabilizing effect, consider a counterfactual scenario: a political crisis in South Korea occurring without a U.S. military presence. North Korea would find it easier to exploit the leadership vacuum in Seoul, potentially staging military demonstrations in the West Sea or attacking ROK units near the demilitarized zone. Even if such actions did not occur, the mere prospect of these risks would significantly destabilize South Korea’s security environment.

More importantly, such uncertainty in and of itself is a critical factor affecting South Korea’s financial markets. Following the declaration and subsequent repeal of martial law, foreign investors withdrew approximately $750 million from the country within three days. Business leaders worry that ongoing instability could lead agencies like Moody’s or Fitch to downgrade South Korea’s national credit rating for the first time since the 1997 Asian financial crisis. However, such worst-case scenarios have not yet materialized. Thanks to the presence of U.S. forces, deterrence remains intact, ensuring a minimum level of stability and predictability.

Challenges Facing the Alliance

The real test of the alliance will come in times of crisis. First, the likelihood of North Korean military provocations continues to rise. Since Donald Trump’s comeback as U.S. president, Kim Jong-un has received signals that diplomacy and dialogue may be possible. Paradoxically, this could encourage more provocations. North Korea might escalate tensions to strengthen its bargaining position ahead of anticipated negotiations or in an attempt to push the Trump administration to prioritize North Korea. During the Biden administration, the odds of substantive negotiations were low, but under Trump an unconventional deal is conceivable. However, it would be naïve to assume that Kim would engage in talks out of gratitude. Instead, provocations such as armed clashes in the West Sea or a seventh nuclear test remain distinct possibilities.

Second, North Korean provocations and subsequent U.S. negotiations could reignite debates over South Korea’s nuclear armament. As defense secretary, Pete Hegseth has already sparked controversy by referring to North Korea as a “nuclear power.” Just hours after his confirmation, President Trump himself echoed this language. These statements have fueled debate in South Korea about nuclear armament, with some experts suggesting that Trump might even tolerate it. Alternatively, the Trump administration could consider redeploying U.S. tactical nuclear weapons. Either scenario would create new challenges for the alliance, as Trump might link South Korea’s nuclear capabilities to a reduction in U.S. troop levels or demand greater financial contributions in exchange for deploying tactical nuclear weapons. Regardless of the specifics, such negotiations could cause friction within the alliance.

Third, tensions within the alliance might arise over China policy. The second Trump administration includes both hawkish figures advocating for strong military engagement and “restrainers” who prefer a more limited U.S. global presence. While these diverse views might create a certain level of tension within the conservative administration, one unifying theme among Trump’s national security team is an aggressive stance toward China. This could lead to expectations that all U.S. allies, including South Korea, contribute to countering China’s influence. The most challenging issue for South Korea would be determining the roles of USFK and the ROK military in a Taiwan contingency. Given the country’s current leadership vacuum, proactive discussions on this issue are difficult. However, failing to address these questions in advance will only make crisis management more difficult if these or other scenarios ever transpire.

Assessing the Risks

Critics might argue that these concerns are overstated. Many experts in both the United States and South Korea remain skeptical that negotiations between Washington and Pyongyang will resume this year. They point out that North Korea has little incentive to curb its nuclear arsenal, especially given its deepening ties with Russia and growing nuclear capabilities. Additionally, the Trump administration has other priority issues, such as curbing mass migration and ending the Russia-Ukraine war. If North Korea has no reason to provoke, then South Korea has no reason to pursue nuclear armament.

Similarly, some Taiwan experts think that tensions in the Taiwan Strait might remain lower than expected. It is widely believed that Trump has little interest in defending Taiwan’s democracy and dislikes committing resources to its defense. For China’s part, Xi Jinping is busy dealing with domestic problems, including an economic recession and military corruption. Thus, as long as the Trump administration does not provoke Beijing, it is unlikely to initiate a major crisis in the Taiwan Strait. As a result, while minor tensions between the United States and China may persist, some analysts argue that the risk of a Taiwan crisis could actually decrease.

However, military alliances cannot base their preparedness on such optimistic forecasts. Strategic planning cannot rely on wishful thinking that assumes nothing will happen. As the saying goes, “prepare for the worst, wish for the best.” The role of military forces is to focus on the former, not the latter. Given that South Korea currently lacks political leadership, and that the U.S. administration is still in its early phase, both countries’ military leaders must recognize these contrasting realities and their potential impact on military preparedness. At the very least, they should engage in discussions about various crisis scenarios to ensure readiness for the potential challenges ahead.

Sungmin Cho is an Associate Professor in the Department of Political Science at SungKyunKwan University in Seoul and a Fellow of the Center for China Analysis at the Asia Society.