Japan and South Korea sit smack bang in the centre of a tightening strategic vice in Northeast Asia, where the long-standing parity between decades old US security guarantees and being dragged into China’s economic orbit is being tested by both Beijing’s growing regional aggression and Washington’s increasingly erratic modus operandi.
For decades, the regional order has rested on a clear division of labour. The United States has provided hard security through formal alliances, forward area troop deployments and nuclear deterrence. At the same time, both Japan and South Korea have leveraged access to global markets - most notably China - to help drive export-led growth. That model as well as once steady links to the US are both under strain.
An estimated 28,500 US troops remain stationed in South Korea under the Mutual Defense Treaty, according to the US Department of Defense, while Japan hosts over 50,000 American troops and support personnel across a network of bases from Okinawa in the south, just east of Taiwan, to Misawa Air Base in the north, 600 miles from North Korea. Together these permanent US troop placements underpin Washington’s Indo-Pacific Command operations.
Crucially, these deployments are not simply legacy arrangements, however, as they also form the operational backbone of deterrence against North Korea and, increasingly, China. It is a reality in Northeast Asia that has repeatedly been seen as key to maintaining a balance of power across the region.
Yet that balance is shifting, and it is only partially the result of Chinese actions. Beijing’s military modernisation, documented in annual Pentagon reports, has accelerated across naval, missile and air capabilities in recent years, with a clear focus on denying US access to the Western Pacific. At the same time, China has long worked at economic integration with both Japan and South Korea – so much so that as of 2026, China is now the largest trading partner for South Korea while Japanese exports to China are approaching 20% of its total and could overtake US exports in the next few years.
This dual dependency in the form of Washington providing the security, with Beijing a key player in regional prosperity, has become increasingly difficult to manage.
And the flashpoint, if it comes, will be Taiwan, the self-governing nation of 24mn still claimed as part of China by Beijing.
US and Japanese defence planning now routinely treats a Taiwan contingency as the primary scenario around which force posture and alliance expectations in the Indo-Pacific should rotate. The Pentagon’s National Defense Strategy identifies Taiwan as the most likely trigger for any major conflict in the region and geography only reinforces that. With Taiwan just over 100 km west of Japan’s Yonaguni Island, a speck of land Tokyo is working to reinforce as a perimeter defence outpost of sorts, sea lanes connecting Japan and South Korea as well as Taiwan to global energy routinely supplies pass through waters already watched day and night by Chinese naval forces.
In the event of such a crisis, neutrality would be almost impossible to sustain as Japanese defence white papers have explicitly linked Taiwan’s security to Japan’s own. Prime Minister Sanae Takaichi in late 2025 also said that any instability in the Taiwan Strait would directly threaten Japanese territory and trade routes. This was a comment that did not go down well in Beijing.
As such, while Japan’s status on any future Taiwan-related conflict is clear, South Korea’s position is more ambiguous even if US bases on the southern half of the peninsula would almost certainly be drawn into logistical or operational support roles.
This creates a structural dilemma for both countries. Both Seoul and Tokyo would face a significant economic punch in the guts should China opt to put a block on imports in the event of conflict – a method Beijing has used in the past with restrictions on South Korean goods coming into the country following the deployment of the THAAD missile defence system by the US in 2017.
Economic coercion by China aside, uncertainty over US policy itself is a major issue both Japan and South Korea are now being forced to ponder, especially in light of US insults aimed at long-standing allies it has failed to pull into its latest military quagmire in the Middle East.
Under Donald Trump’s previous administration, alliance commitments were frequently framed in transactional terms, with demands for increased host-nation support payments and periodic suggestions that troop withdrawals were under consideration. While many of these proposals were not fully implemented, they did introduce a degree of doubt about the long-term reliability of US guarantees.
And now, under Trump’s second administration, one built atop a tower of diplomatic playing cards always wobbling and looking like collapse is imminent, grandstanding is too often given priority over structural discipline. Because of this, things look a lot worse.
Even limited ambiguity in US commitments and statements of intent criticising allies, can have outsized effects on planning. Concepts such as whether or not the current US assets stationed in Korea would remain dedicated to peninsula defence in the event of an attack by North Korea are being openly questioned – and doubted.
If US engagement remains consistent, both Japan and South Korea as well as Taiwan are likely to remain embedded within a US-led deterrence plan. All three countries would expand their roles as operational partners.
However, a much more volatile possibility emerges if US policy becomes less predictable - as is being seen. Should any level of US troop withdrawal take place or inconsistent signalling from Washington continue, both Japan and South Korea would, sensibly, start to look to a time when the US can no longer be trusted.
Japan would likely accelerate its ongoing military build-up and deepen ties with other regional partners such as Australia and India, as seen in frameworks like the now largely defunct Quad, an informal grouping essentially put out of action by the US. South Korea meanwhile would face a much sharper trade-off, given its proximity to North Korea and deeper economic links to China.
Tokyo could even reconsider its self-imposed long-standing constraints on military power, including debates over nuclear deterrence. South Korea, already within range of North Korean artillery and missiles, is one of the world’s leading nations in terms of nuclear know-how and may be forced to walk down the same path.
For China though, any reduced US presence in Northeast Asia would essentially signal victory while expanding Beijing’s strategic space. The deterrence balance in the Taiwan Strait would shift, increasing the feasibility of coercive measures against Taipei and the possibility of outright invasion would not be such a remote concept.
Northeast Asia, thanks to the ever erratic 47th occupant of the White House, is fast becoming a region where stability depends less on alliances and more on perceptions of credibility.
The role of Japan and South Korea is becoming more fluid and more precarious. China’s rise is a constant, measurable in defence budgets and industrial capacity, but US policy is increasingly variable, shaped by domestic politics, transactional needs, and at times which side of the bed its leader wakes up on.
No comments:
Post a Comment