What would happen if the US scales down its military presence in South Korea, and how could it impact deterrence against North Korea?

A report from the Wall Street Journal (WSJ) claims that Washington is considering scaling back its military presence in South Korea. However, reports from Seoul indicate that the South Korean Defence Ministry have not received any formal communication from Washington.

If the reports were to be true, Washington is reviewing proposals to withdraw approximately 4500 troops from South Korea. There are approximately 28,500 troops stationed in South Korea, part of the United States Forces Korea (USFK). These forces serve as a critical deterrent to the nuclear-armed North Korea. They organise and participate in joint operations and drills as part of trilateral security cooperation between the United States, South Korea and Japan.

The report at WSJ also states that Washington is planning to relocate these forces to other parts of the Indo-Pacific region, such as Guam. Even though no concrete official reports confirm this, Trump's rhetoric indicates the same. Trump historically called South Korea a ‘money machine’ in October before his second term at the White House. He insisted back then that if he were to be the next President, South Korea would have to pay billions more to host the American Army.

The US and South Korea agreed on a new deal which sees the cost of deploying the US army in South Korea rise by 8.3 per cent to $1.1 billion in 2026.

North Korea's growing threat

A senior researcher of Carnegie Endowment, an international think tank, states that North Korea is in the ‘strongest strategic position in decades’. According to the intelligence report of the United States Defence Intelligence Agency, '2025 Worldwide Threat Assessment', North Korea is most certainly in a position to launch a prolonged war. It has now developed an intercontinental ballistic missile (ICBM) capable of reaching the continental United States. Military experts in South Korea believe that it is actively receiving aid from Russia, including military cooperation, SA-22 surface-to-air missile systems, and electronic warfare equipment. It is also reciprocating by providing military and material support to Russia against Ukraine. These two nations also signed a Comprehensive Strategic Partnership agreement last year. Frequent missile tests and provocative actions have heightened tensions in the region. On the other hand, North Korea’s critical economic and political dependence on China underpins the bilateral relationship between these two. The presence of US military troops acts as a deterrent to hinting to Pyongyang that any aggression would be reciprocated with a strong military response.

South Korea's Military Autonomy

South Korea ranks 5th in the 2025 Global Firepower Index, with advanced weaponry, military readiness, and cybersecurity. It isn't entirely dependent on the US for deterrence. It allocates $222 billion to defence spending.

It has a Three-Axis Defence System comprising of Kill Chain preemptive strike strategy, a multi-layered Korea Air and Missile Defence System, and Korea's Massive Punishment and Retaliation doctrine. It also has other advanced weaponry, such as a fleet of F-35 stealth fighters, Hyunmoo-5 ballistic missiles capable of penetrating underground bunkers. It has indigenously developed AI-powered military tech that enables drones and fighter jets to fly autonomously.

"Territorial defence can no longer rely solely on human resources,” said Seong Tae Jeong, chief technology officer at the Advanced Defence Science and Technology Research Institute at South Korea’s Agency for Defence Development

South Korea and Japan have been working towards less reliance on the US, as Japan's Prime Minister Ishiba Shigeru was pushing for an ‘Asian NATO’- a long-term strategy for a viable ally in the region.

Despite not having its nuclear arsenal, it comes under the US nuclear umbrella. Seoul does have civil nuclear technology and a missile system capable of delivering a payload if it ever chooses to pursue nuclear ambitions.

Deterrence Dynamics and Risks

Maintaining a credible deterrent in the face of North Korea’s nuclear ambitions remains a challenge for the United States. Indo-Pacific Security Initiative (IPSI), with the support of the Defence Threat Reduction Agency, produced a report on the United States' readiness for deterrence in the region. The report's striking findings indicate that if a conflict starts with China or North Korea, the United States will not be able to deter the other one either North Korea or China from escalating the conflict. What could start from one flash point could escalate into much more. The US-South Korea conflict with North Korea could quickly spill into a Nuclear War. Other flashpoints, like Taiwan, is also facing growing military, diplomatic, and information pressure from China towards its long-term objective of unification. North Korea continues to support its nuclear weapon program by increasing its plutonium and highly enriched uranium, adding to its arsenal.

Gen. Xavier T. Brunson, commander of United Nations Command, Combined Forces Command and United States Forces Korea, met with Gen. Ken-ichiro Nagumo, commander of the Japanese Joint Operations Command, on May 20.

Brunson reiterated that USFK is committed to maintaining the momentum of trilateral cooperation. "The partnership between the United States, the Republic of Korea, and Japan is evolving beyond confidence-building measures and is maturing into a cornerstone of regional stability", stated Brunson.

However, scaling back does not necessarily mean a reduction in deterrence; the US could possibly justify this scaling down by citing the advanced technology and increased military spending of South Korea. Still in South Korea, this reduction might spark the debate of having its own nuclear arsenal and stepping out of the US umbrella. Domestically, this will resonate with the USA's ‘America first’ policy.

Nonetheless, this potentially emboldens China and North Korea, destabilising the balance of power in the region. Beijing might pursue its expansionist ambitions and push territorial integrity of Taiwan if the US seems increasingly adamant about its ‘America first’ policy. In a conflict situation, the United States is likely to face operational and strategic challenges in the Indo-Pacific and the Korean Peninsula.