Trump Reshapes US-South Korea Alliance Over Defence, Trade and North Korea, Washington

Washington, 18 August (Brussles Morning Newspaper) The US-South Korea relationship has survived wars, political upheaval and repeated crises with North Korea. Under Donald Trump, however, the alliance has increasingly been treated as something to renegotiate — not only over security, but over who pays, how forces are used and what Washington expects from Seoul in return.

That tension has returned to the surface after Trump instructed the Pentagon to “substantially reduce” US participation in joint military exercises with South Korea. He cited their cost and Seoul’s refusal to take part in US actions against Iran, bringing a fresh dispute into a partnership that has anchored security on the Korean Peninsula for more than seven decades.

Why Trump wants to scale back military exercises

The immediate disagreement centres on Ulchi Freedom Shield, the annual exercise involving US and South Korean forces.

The drills began on 17 August and involve about 18,000 South Korean troops. They are designed to prepare the allies for a range of threats, including missile attacks, drones, cyber warfare and GPS disruption.

Trump’s objections are not new. During his first presidency, he repeatedly complained about the cost of large-scale exercises and questioned why Washington should carry such a significant financial burden.

South Korean President Lee Jae Myung has taken a different view. On Tuesday, he called for stronger independent South Korean defence capabilities but stressed that the current exercises are defensive and are not intended to threaten North Korea.

The disagreement illustrates a recurring feature of Trump’s approach: he supports the alliance, but expects Seoul to shoulder more of the cost and responsibility for its own security.

From threats against Kim Jong Un to face-to-face diplomacy

Trump’s handling of North Korea has also transformed the political atmosphere surrounding the alliance.

In 2017, Trump and North Korean leader Kim Jong Un exchanged increasingly confrontational rhetoric as concerns grew over Pyongyang’s nuclear and missile programmes. Months later, the confrontation gave way to an extraordinary diplomatic opening.

Trump met Kim in Singapore in June 2018, becoming the first sitting US president to meet a North Korean leader. He subsequently suspended major military exercises with South Korea as negotiations continued.

The breakthrough did not produce a lasting nuclear agreement. A second summit in Hanoi in February 2019 collapsed without a deal, and North Korea continued developing its weapons programmes.

Yet Trump has not abandoned his preference for direct diplomacy. On 17 August, he said Kim had responded to his latest overtures, although he gave no details about what the North Korean leader had communicated.

Lee has also sought room for diplomacy. In June, he said Trump was open to considering a phased approach that would initially focus on halting North Korea’s nuclear and missile programmes while retaining denuclearisation as a longer-term objective.

Defence spending has become harder to separate from politics

Money has long been part of alliance negotiations, but Trump has made it far more politically visible.

He has repeatedly argued that South Korea should contribute more towards the cost of maintaining American forces on the peninsula. For Seoul, the challenge is to respond to those demands without weakening the US military commitment that remains central to its defence strategy.

Lee’s government is simultaneously pushing for greater South Korean military autonomy, including stronger domestic capabilities and greater operational responsibility.

The result is a US-South Korea relationship in which questions about deterrence are increasingly tied to questions about cost, responsibility and national self-reliance.

Trade is now almost as important as troops

Trump has also broadened the pressure on Seoul beyond defence.

Tariffs and investment have become major parts of the relationship, particularly as Washington seeks to bring manufacturing and strategically important supply chains into the United States.

The White House said following Trump’s October 2025 state visit to South Korea that the two countries were opening a “new chapter” in their alliance. Their agreements covered industries including shipbuilding, semiconductors, energy, pharmaceuticals, critical minerals and advanced technology.

The framework included $150 billion in approved Korean investment in US shipbuilding and another $200 billion in planned strategic investment. The two governments also set out tariff arrangements affecting South Korean goods entering the US.

That means disagreements that were once largely about troops and North Korea now extend deep into trade and industrial policy.

Why the alliance still matters

For all the friction, Washington and Seoul remain closely tied.

North Korea continues to possess nuclear weapons and develop missile capabilities, while its growing relationship with Russia has added another layer of uncertainty to regional security.

For South Korea, the American security commitment remains difficult to replace. For Washington, South Korea remains an important strategic partner in the Indo-Pacific and a major industrial and technological partner.

Trump has therefore not dismantled the alliance. He has changed the terms of the conversation around it.

The US-South Korea relationship increasingly reflects his broader approach to alliances: longstanding partnerships remain valuable, but their costs, benefits and obligations are repeatedly put back on the negotiating table.

What happens next?

The first question is how far the Pentagon will go in implementing Trump’s instruction to reduce joint exercises and whether that change extends beyond the current drills.

The second is North Korea. Trump’s claim that Kim has responded to his outreach raises the prospect of renewed contact, but there is no confirmed summit or new nuclear agreement at this stage.

For Lee, the task is more immediate: strengthen South Korea’s ability to defend itself without allowing greater military independence to be interpreted as a weakening of the alliance.

After more than 70 years, Washington and Seoul remain allies. What Trump has changed is the assumption that the practical terms of that alliance can be taken for granted.