Since the United States and Israel launched major military strikes against Iran in February, America’s allies have faced mounting pressure to support a conflict that is widely unpopular. As a result, the Trump administration has shown an increasing willingness to punish allies it considers insufficiently supportive of its Iran policy. In recent months, Washington has halted trade with Spain, publicly clashed with Italian Prime Minister Giorgia Meloni, criticised Britain and France for their reluctance to back military action, and threatened to bomb Oman.
The latest target of the president’s petulance is South Korea. In August, Donald Trump ordered the Pentagon to scale back joint military exercises with Seoul, citing their financial cost and describing the drills as “inappropriate and hostile” toward North Korea.The announcement was consistent with two longstanding features of Trump’s foreign policy: his resentment over the cost of American alliances and his desire for closer relations with North Korea.
Trump has repeatedly complained that the United States spends “tens of billions of dollars” defending its allies while receiving little in return. In an interview with Fox News, he argued that Seoul should remember that “we have 40,000 troops in South Korea,” although the actual figure is closer to 27,000. South Korea currently pays Washington around $1 billion annually toward the cost of stationing American forces in the country, far short of Trump’s demand for $5 billion a year.
Trump has also continued to speak warmly of North Korean leader Kim Jong Un, boasting of their “great relationship” and saying that Kim has always treated him with “great respect.” Trump has argued that reducing joint exercises with South Korea would make the peninsula “much safer,” declaring of Kim: “I understand him and he understands me.”
However, in announcing the reduction in military exercises, Trump explicitly drew attention to Seoul’s refusal to support his Iran policy. “Somewhat unrelated,” he said, “I recently asked the President of South Korea if they would like to join us in the denuclearization of the Islamic Republic of Iran, and they said, ‘No thanks!’”
Yet South Korea has good reason to avoid involvement in the conflict. Since the beginning of the war, “no noncombatant country has been hit harder than South Korea,” according to the Center for Strategic and International Studies. South Korea depends on shipments through the Strait of Hormuz for around 70% of its oil and 20%of its natural gas. The conflict directly threatens the country’s energy security, while its broader objectives remain unclear. It is also worth noting that the Strait of Hormuz – whose reopening Trump has cited as an American war aim – was open before the conflict began.
Nevertheless, the Trump administration’s decision should concern both Seoul and Washington. Joint military exercises are not just training operations; they are a demonstration of the United States’ commitment to South Korea under their longstanding defence alliance. Alongside the presence of American troops, they form an important part of the deterrence intended to convince Pyongyang that an attack on Seoul would draw an American response.
Scaling back those exercises does not mean that Washington has abandoned its commitment to defend South Korea. But when the decision is accompanied by Trump’s repeated complaints about the alliance, it introduces uncertainty into a relationship whose deterrent power depends heavily on credibility.
That uncertainty should concern Washington as much as Seoul. As confidence in the United States has weakened, South Korea has begun placing greater emphasis on relationships with other regional powers. In January, Lee became the first South Korean president since 2019 to visit China, where he called for a “new phase” in the bilateral relationship and a “full-scale restoration of South Korea-China relations.” By August, China’s top diplomat, Wang Yi, was declaring that bilateral relations had “fully recovered.”
Lee has also made improving relations with North Korea a central foreign-policy objective, including pursuing a formal end to the Korean War. Any meaningful diplomatic breakthrough, however, will require limiting the advancement of North Korea’s nuclear programme. This gives China an important role. Beijing remains Pyongyang’s most important economic and diplomatic partner, which Seoul hopes can be used to bring North Korea to negotiations. This creates an uncomfortable dynamic for Washington. China and South Korea are hardly natural strategic partners, and the presence of American forces on the Korean Peninsula has long been a source of tension between Beijing and Washington.
It remains unlikely that South Korea would abandon its alliance with the United States or seek the withdrawal of American forces in the near future. However, if Seoul comes to believe that Washington’s security guarantee is conditional on supporting American conflicts elsewhere, closer relations with Beijing become more attractive.
Despite their longstanding historical grievances, South Korea is also pursuing closer relations with Japan. Driven by shared concerns about Washington’s reliability, regional instability and Beijing’s growing power, Seoul and Tokyo have deepened their cooperation. This points to a broader danger in Trump’s approach to alliances. Alliances cannot simply be neglected for four years and then restored when a new president enters the White House. Governments adapt to uncertainty: they build new relationships and reduce their reliance on partners they no longer consider dependable.
With more than two years of Trump’s presidency remaining, these changes could become increasingly difficult to reverse. His successor will inherit an alliance system in which countries rely less on American support. In South Korea’s case, this could mean developing a more autonomous network of relationships across Northeast Asia, built around closer ties with Japan, greater engagement with China and attempts to establish a more direct relationship with North Korea. By the time Trump’s successor enters the White House, the challenge may not simply be repairing America’s relationship with South Korea. Instead, it may be convincing Seoul that Washington should remain its security partner of choice.
Recommended Readings:
Cha (2026) Strategic Clarity: Reassessing the Value of China to Korea.
Kelly (2026) Trump questions South Korea alliance as Kim responds.
Sneider (2026) The Trump effect on Japan-South Korea relations.