This month, South Korea and the US staged their latest joint naval drills. Destroyers and patrol aircraft rehearsed responses to potential incursions by North Korean drones and special forces across the maritime border.
“With the overwhelming power of the South Korea-US combined fleet, we will strongly retaliate against any enemy provocation,” South Korean navy commander Ryu Yoon-sang declared.
But behind the boilerplate expressions of common resolve, experts describe a series of possible crises brewing in US-South Korea relations. Despite an alliance that goes back decades, the two countries are threatening to diverge on sensitive questions of trade, regional security and the growing North Korean nuclear threat.
When US President Donald Trump announced a 25 per cent “reciprocal” tariff on Korean imports, South Korean officials were shocked. They had believed a long-standing, comprehensive free trade agreement under which South Korea in effect does not levy tariffs on American goods would set them apart.
Policymakers in Seoul also worry that America’s fixation on the rise of China will lead it to neglect deterrence efforts against Pyongyang, while also pressuring South Korea into a more confrontational stance towards Beijing.
While many of these fears reflect long-standing tensions, they have been exacerbated by the return to power of Trump, whose repeated declarations of admiration for North Korean dictator Kim Jong Un stand in contrast with his often contemptuous attitude towards the South.
During his first term, Trump threatened to pull out of the Korea-US (Korus) free trade agreement that came into force in 2012, and to withdraw US troops from the Korean peninsula in a dispute over cost-sharing. The fact that South Korea has a record trade surplus with the US has only added fuel to the fire.
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Since returning to office in January this year, Trump has declared his intention to reopen negotiations with Kim, fuelling South Korean fears of a deal between Washington and Pyongyang over Seoul’s head that could leave it even more vulnerable to North Korean nuclear blackmail.
And South Korean anxieties have been compounded by economic weakness and political instability at home. Even before then-president Yoon Suk Yeol’s ill-fated declaration of martial law in December, growth in Asia’s fourth-largest economy was slowing amid persistently weak domestic demand and intensifying competition from China.
Seoul’s ability to respond to these escalating challenges has been undercut by the prolonged political crisis that followed the martial law debacle.
Yoon was removed from office by South Korea’s constitutional court in April, and this month both acting president Han Duck-soo and finance minister Choi Sang-mok resigned within hours of each other. That has left the country in the hands of a weak caretaker administration led by the education minister until fresh presidential elections are held next week.
The frontrunner, leftwing opposition leader Lee Jae-myung, has in the past described the US as an “occupying force”, and more recently advocated for South Korea to take a more conciliatory line with China.
Whether Lee or his conservative challenger Kim Moon-soo prevail, highly sensitive discussions that have been put on hold in recent months cannot be postponed for much longer. The results could have ramifications for economic and security relationships across east Asia.
“The alliance is in a state of quiet crisis that few people have noticed,” says Victor Cha, a former White House official and Korea chair at the Center for Strategic International Studies (CSIS) think-tank in Washington. “But . . . the crisis is unlikely to remain quiet for long.”
At first, South Korean officials were confident they would be spared the worst of the US president’s aggressive trade policies, Seoul-based diplomats recall.
In addition to their long-standing security relationship, dating back to the Korean war, and the trade agreement, Korean companies including chipmaker Samsung and auto giant Hyundai are investing tens of billions of dollars in manufacturing facilities in the US.
But that illusion was shattered in March, when Trump singled South Korea out for censure during his State of the Union address. Claiming falsely that the east Asian country imposes tariffs “four times higher” on the US than vice versa — because of the free trade agreement, the correct number is in effect zero on both sides — the US president suggested that Seoul was benefiting unfairly. “We give so much help militarily and in so many other ways to South Korea,” Trump said. “This system is not fair to the United States and never was.”
Since then, Korean exporters have been hit by Trump’s tariffs on steel and autos, and are bracing themselves for levies that target chips, smartphones and pharmaceuticals. Trump’s “reciprocal” 25 per cent tariff rate is suspended only until July.
“Korean officials were extremely disappointed and dismayed by the fact that they were assigned such a high tariff rate,” says Wendy Cutler, a former US trade official who helped negotiate the Korus pact and is now vice-president of the Asia Society Policy Institute think-tank.
“That said, they’re pragmatic, and given their security alliance they have no choice but to work with this administration,” Cutler adds.
Korean efforts to resolve tensions have been severely hampered, however, by prolonged political turmoil at home. According to several people familiar with the ongoing talks between US and Korean officials, last month then acting president Han made a push for a quick deal that he could present to the South Korean electorate before standing in June’s election himself. Trump administration officials also hoped for a speedy agreement, which they could present as evidence that the US president’s economic brinkmanship was yielding quick results.
But those hopes were dashed after it became clear that Han did not have the political authority to deliver a deal that would have bound the hands of his elected successor. When he and Choi both resigned, the prospect seemed dead.
Even if high-level talks resume as expected soon after the election, observers note that they could yet prove contentious.
Potential outcomes include South Korea securing some degree of tariff relief by demonstrating willingness to reduce its trade surplus, including by buying more US liquefied natural gas. The two countries also hope to secure an arrangement for Korean shipbuilders to build vessels for the US Navy, and Seoul has signalled willingness to address US concerns over a range of Korean non-tariff barriers.
But people with knowledge of the talks privately acknowledge the proposals under discussion are unlikely to make a significant short-term dent in South Korea’s trade surplus in goods with the US, which is now $55bn.
Chul Chung, president of the Korea Economic Research Institute, says Trump’s July tariff deadline may prove “too tight” for a new administration in Seoul.
“Making a deal too early is not a good strategy, as it would give other countries a benchmark against which they could negotiate something better,” Chung says. “But if we wait too long, we could end up without any bargaining power.”
“We have known for some time that economic over-dependence on China was a risk,” says a former senior Korean government official. “But now we know that over-dependence on the US is a risk for us too.”
For many South Koreans, the potential for trade tensions to spill over into the defence alliance with the US is even more concerning.
“Our economic relations are a matter of richer or poorer, but our security relations are a matter of life or death,” says Yeo Han-koo, a former South Korean trade minister now at the Peterson Institute for International Economics think-tank in Washington.
Trump has publicly linked the two, writing in a social media post last month that he had discussed “payment for the big time Military Protection we provide to South Korea” in a call with then-acting president Han.
“We are bringing up other subjects that are not covered by Trade and Tariffs, and getting them negotiated also. ‘ONE STOP SHOPPING’ is a beautiful and efficient process!!!” Trump wrote.
While Trump is expected to demand that Seoul make a larger financial contribution to the presence of the 28,500 US troops stationed on the peninsula — it will pay 1.52tn won ($1.19bn) in 2026, up 8.3 per cent from 1.4tn won in 2025, in a deal renegotiated just before the US election — more concerning for many analysts is what appears to be a growing divergence of views on the purpose of their defence relationship.
Clint Work, a fellow at the US National Defense University, a research institution affiliated with the Pentagon, notes that whereas South Korea has historically insisted the alliance be focused on the threat from North Korea, the US increasingly views this as secondary to the risk of a Chinese invasion of Taiwan.
Elbridge Colby, now a senior official in charge of overseeing policy development at the Pentagon, told South Korean media in May last year, while out of office, that “South Korea is going to have to take primary, essentially overwhelming responsibility for its own self-defence against North Korea because [the US doesn’t] have a military that can fight North Korea and then be ready to fight China”.
“The fundamental fact is that North Korea is not a primary threat to the US,” he added.
That may result in Washington intensifying pressure on Seoul to consent to US troops being redeployed or rotated elsewhere in the region as Washington sees fit.
“South Korea has two great fears: either that it will be abandoned by the US to face North Korea alone, or that the US will rope it into a war with China,” says Work. “Washington shifting attention from North Korea to Taiwan touches both these nerves at once.”
Says Cha of CSIS: “It is almost inconceivable to me that there won’t be some adjustment to the US force posture in Korea, and they may inform rather than consult the South Koreans about it.”
Speaking on condition of anonymity, a US official in Korea says that the policy now being pursued within the Pentagon is “100 per cent” in line with Colby’s previous remarks. They add that the outcome of talks between on the alliance, including those on cost-sharing, would determine whether American troop numbers go up or down — noting that maintaining the status quo was the “least likely option”.
While this will probably prove uncomfortable for whoever wins next week’s presidential election, analysts say tensions could be particularly acute in the event of a victory for leftwing frontrunner Lee, who insists that South Korea has no direct interest in the outcome of a conflict involving Taiwan.
“We must keep our distance from a China-Taiwan contingency, if such a crisis should occur,” Lee said during a television debate this month. “We can get along with both China and Taiwan.”
Work says a Lee administration could find common cause with the Trump administration if a modest reduction of US troops in South Korea were presented in terms of Seoul assuming more responsibility for its own defence — something that has been a goal of successive leftwing governments.
But that would probably provoke a backlash from Korean conservatives. And members of both the US and South Korean military establishments remain doubtful about South Korean armed forces’ readiness to assume a leading role in confronting the North, says Work.
He notes that many on the South Korean left have long argued that the US maintains a troop presence on the peninsula not just for South Korea’s benefit but for its own “broader hegemonic goals”.
“This has contributed to a sense that you can push back hard against the Americans, because they’ll never actually leave,” Work explains.
“But if all of a sudden you realise that the Americans really are prepared to leave, that could have a very sobering effect.”
If Trump showing less interest in deterring North Korea militarily creates a dilemma for the South, the prospect of him re-engaging with Pyongyang diplomatically could prove even more frightening.
During his first term, Trump became the first sitting US president to meet a North Korean leader, although talks between the two sides eventually collapsed in 2019.
Since then, North Korea’s nuclear weapons programme has gone from strength to strength. Kim has also been emboldened by his blossoming relationship with Russian President Vladimir Putin since Moscow’s full-scale invasion of Ukraine in 2022 — North Korean troops were sent to fight Ukrainian forces — and by Russia and China’s waning commitment to enforcing UN sanctions against Pyongyang.
“North Korea is significantly more capable, has more nuclear warheads and can threaten the US and its allies in more credible ways than it was positioned to do when Trump first took office in 2017,” says Ankit Panda, a nuclear weapons expert at the Carnegie Endowment for International Peace think-tank in Washington. By contrast, South Korea does not possess nuclear weapons.
Panda is one of a growing number of defence experts who argue that rather than continuing to insist on the North’s denuclearisation as a condition for meaningful diplomatic engagement, Washington and Seoul should instead pursue a more realistic objective — agreeing arms control and other risk-reduction measures with Pyongyang.
Such an approach is regarded as anathema by South Korean officials, who worry this would tacitly accept North Korea’s right to possess nuclear weapons.
The Trump administration is currently reviewing its North Korea policy. But while official statements have so far restated the US commitment to pursuing denuclearisation, Trump and officials including secretary of defence Pete Hegseth have also referred to the North on several occasions as a “nuclear power” — a phrase that sounds alarm bells in Seoul.
In March, Trump claimed that his administration was already in “communication” with Pyongyang, describing the North as a “big nuclear nation”, and Kim as a “very smart guy”.
Jenny Town, a senior fellow at the Stimson Center think-tank in Washington, says that “one of South Korea’s nightmare scenarios” would be Trump cutting a deal with Kim that involves North Korea halting or scrapping its intercontinental ballistic missile programme, but retaining its shorter-range missiles and the ability to produce nuclear warheads.
Such an outcome would reduce or eliminate Pyongyang’s capacity to threaten the US, while allowing it to continue or intensify its nuclear threats against the South.
“South Korea worries that Washington and Pyongyang will cut them out of the process altogether,” says Town, “They have good reason to be concerned, given that Trump and Kim both seem much less interested in consulting them than last time round.”
Cha of CSIS adds that, if this were to happen, growing demands within South Korea for the country to acquire its own nuclear weapons might prove unstoppable — a scenario that would spark a wider security crisis throughout Asia and beyond.
“It’s not even going to be a debate any more,” he says.
