Over the past two decades, the nature of the United States’ alliances with Japan and South Korea has undergone a marked evolution. Once heavily tilted in favour of American strategic interests and characterised by an asymmetrical power dynamic, these relationships are now transitioning into more balanced – though still complex – partnerships. However, as these ties deepen and trans-Pacific ties increase, the long-standing problem of a significant US troop presence on both Japanese and South Korean soil remains. With it comes increased public scrutiny and political discomfort, particularly when measured against a backdrop of recurring criminal incidents and questions of sovereignty.

Bases, troops, and uneasy hosts

To grasp the full dimension of the US role in Northeast Asia, one must first consider the sheer scale of its military footprint. Japan hosts approximately 54,000 US troops on its soil, the largest contingent of American forces anywhere outside the continental United States. The bulk of them are stationed in the Okinawa islands which account for less than 1% of Japan’s total landmass but hosts more than 70% of the US military facilities in the country. South Korea, for its part, accommodates almost 29,000 US troops, most notably at Camp Humphreys – the largest US overseas military base in the world, located south of Seoul.

These deployments are the physical backbone of America’s forward deterrence posture in the Indo-Pacific, yet their presence is far from uncontroversial. In both countries, local opposition has been inflamed not only by environmental and sovereignty concerns but also by the long and troubling history of crimes committed by US troops against host nation civilians – primarily young women.

Incidents ranging from theft and assault to more egregious acts like rape and murder have periodically reignited public anger. The 1995 abduction and gang rape of a 12-year-old Okinawan girl by three African-American servicemen became a flashpoint in Japan, prompting massive protests and renewed calls for a reduction in the US presence.

Five years later in South Korea, the 2002 Yangju highway incident, in which two Korean schoolgirls were crushed to death by a US military vehicle, led to nationwide protests and demands for justice – particularly as the US troops involved were found not guilty of negligent homicide.

While both governments have sought to mitigate these tensions through Status of Forces Agreement (SOFA) revisions and public apologies, the fundamental unease remains. Critics point to what they describe as insufficient accountability under SOFA provisions, which often shield US personnel from local jurisdiction unless the alleged crime occurs off duty and off base.

Dependents to partners in deterrence

Against this contentious backdrop, the security partnerships themselves have transformed considerably. In the early 2000s, both Japan and South Korea were widely seen as strategic outposts – effectively glorified staging grounds – for American military logistics and power projection. Their defence postures were premised on a heavy reliance upon US extended deterrence, especially in light of the growing nuclear and ballistic missile threats posed by North Korea.

However, as regional dynamics shifted – with China’s rise and North Korea’s continued provocations – both Tokyo and Seoul began reassessing their domestic military strategies. Japan, led by figures such as the late Prime Minister Shinzo Abe, initiated a steady dismantling of its pacifist constraints.

By reinterpreting Article 9 of its constitution, Tokyo permitted collective self-defence and expanded the operational scope of its Self-Defense Forces (SDF), culminating in record-breaking defence budgets and increased interoperability with US forces.

South Korea, too, has invested heavily in its military capabilities, including indigenous missile defence systems and advanced aircraft procurement. Despite occasional frictions – particularly under progressive administrations wary of aligning too closely with Washington – Seoul has participated in numerous joint drills and strategic dialogues, reflecting a deepening, if sometimes ambivalent, defence partnership.

Strategic convergence, but diverging priorities

This dual evolution reached a symbolic high point with the 2023 Camp David summit, where the leaders of the US, Japan and South Korea pledged to enhance trilateral cooperation on regional security, cyber defence and supply chain resilience.

The fact that Tokyo and Seoul could momentarily set aside their deeply rooted historical animosities to pursue a common strategic vision marked a significant, if fragile, turning point.

Nonetheless, underlying tensions remain. Japan views China as its principal long-term adversary, particularly due to territorial disputes in the East China Sea and concerns over Taiwan. South Korea meanwhile maintains a more nuanced posture toward Beijing given its proximity, balancing security concerns with economic pragmatism. This divergence in threat perception often hampers the creation of a seamless, trilateral security framework – though North Korean provocations do tend to unify the trio on a temporary basis from time to time.

Economic integration

Beyond defence, the US, Japan and South Korea have increasingly positioned themselves as economic allies in the broader strategic contest with China. With the disruptions wrought by the COVID-19 pandemic in recent years and the growing urgency to "de-risk" from Chinese supply chains, Tokyo and Seoul have become vital players in Washington’s Indo-Pacific Economic Framework (IPEF) and other initiatives aimed at reshaping global trade flows.

Both countries have heavily invested in semiconductor manufacturing, clean energy technologies, and critical mineral sourcing – sectors central to US strategic interests. To this end, the economic dimension of these partnerships now rivals the military one in importance. The growing convergence of tech standards, industrial policy, and strategic investment underlines the shift from traditional alliance structures toward more holistic strategic cooperation.

Enduring civilian cost

Yet as the geopolitical calculus shifts and defence budgets increase, the human cost of hosting a permanent foreign military presence is increasingly coming to the fore. The frequency of crimes committed by US servicemen in Japan and South Korea may be statistically low relative to their numbers, but their symbolic weight is immense. Each incident reignites debates about national dignity, judicial sovereignty, and the limits of alliance loyalty.

Public opposition in Okinawa has intensified in recent years, with polls consistently showing a majority of residents favouring a reduction, if not total removal, of US bases. In South Korea, civic groups and student movements have periodically rallied against the presence of US troops, especially during periods of heightened nationalistic sentiment or friction over burden-sharing negotiations. And with the potential for basing US troops in the Pacific in Taiwan to the south all but off limits for fear of direct confrontation with Beijing, Washington can do little but offer appeasement to their host nations in the region.

Despite these issues, however, both Tokyo and Seoul have largely maintained their strategic alignment with Washington even if the delicate balance – between strategic necessity and public grievance – is likely to persist.

As both countries continue to mature into more autonomous defence-minded entities in the Northwest Pacific, they may demand greater equality and transparency within the alliance structure, including greater say over how US forces are stationed and governed. Yet the old shadows of occupation, crime, and unbalanced authority linger, reminding both Seoul and Tokyo – as well as Washington – that there are still outstanding issues that must be addressed with honesty and mutual respect to allow the US-Japan-South Korea trilateral relationship to reach its full potential.