Past tensions continue to shadow South Korea-U.S. alliance

A 2020 Security Consultative Meeting (SCM) between South Korean and U.S. defense chiefs in Washington is often viewed as a clear example of strain within the alliance.

The joint statement issued after the talks omitted a routine reference to maintaining the size of U.S. Forces Korea. Public remarks also reflected a tense atmosphere, with then-South Korean Defense Minister Suh Wook calling for an accelerated transfer of wartime operational control, while then-U.S. Defense Secretary Mark Esper said the conditions for such a transfer had yet to be met.

Tensions were further underscored when a scheduled joint press conference was canceled just three and a half hours before it was set to begin, with no explanation from either side. Details of the internal exchanges later emerged in Esper’s memoir, published two years afterward.

In it, Esper wrote that he sharply criticized the Moon Jae-in administration in closed-door discussions, accusing it of failing to properly manage the THAAD missile defense site in South Korea. He also questioned, “Is this how an ally behaves?” At one point, he said he directed then–U.S. Joint Chiefs of Staff Chairman Mark Milley, who joined by video conference, to consider reviewing THAAD deployment options.

The friction, he wrote, had been building for years. Esper said he had repeatedly raised concerns from 2018 over conditions at the THAAD site for U.S. troops, arguing that Seoul had not responded adequately.

Other senior U.S. officials voiced similar frustrations. Former National Security Advisor Herbert McMaster later wrote that differences between Seoul and Washington were already evident during President Moon Jae-in’s 2017 visit to the United States, particularly over North Korea policy. Former Secretary of State Mike Pompeo also criticized the Moon administration’s North Korea approach in his memoir.

Taken together, key figures in the Trump administration’s national security team described growing distrust toward Seoul. McMaster and Esper both had tense relations with then-President Donald Trump, who was often skeptical of alliances, making the widening gap with South Korea more notable.

During periods when Moon and Trump aligned on North Korea diplomacy, those tensions were largely contained. But after the collapse of the 2019 Hanoi summit, accumulated mistrust became more visible, culminating in the 2020 SCM meeting.

The early months of the Lee Jae-myung administration have taken a somewhat different approach. Before visiting the United States, Lee traveled to Japan first, signaling support for closer trilateral coordination among South Korea, the United States and Japan, a move widely seen in Washington as reassuring.

Still, frictions have surfaced. Disputes over access control in the Demilitarized Zone and a temporary U.S. restriction on intelligence sharing following a classified information leak controversy have periodically strained coordination.

At the same time, analysts say managing ties with U.S. President Donald Trump remains challenging given his transactional approach to alliances, while South Korea has limited room to distance itself from Washington.

Under these conditions, observers say stronger internal coordination is needed to prevent policy disagreements from spilling into broader alliance tensions. Yet signs of disunity have emerged within the government.

Unification Minister Chung Dong-young, who was at the center of the classified information controversy, recently questioned the intent behind public discussion of the issue, a remark that highlighted divisions within the foreign policy and security establishment between hardline and engagement-oriented camps.

Signs of misalignment are also emerging between foreign policy and trade policy. During a recent Cabinet meeting, President Lee reportedly instructed Industry Minister Kim Jung-kwan to coordinate with the National Security Office and Foreign Ministry before engaging with the United States, urging officials to “get along better.”

The remark reflected concerns that ministries were competing for influence in sensitive negotiations with Washington, particularly over U.S.-bound investment discussions.

Analysts warn that such coordination gaps could complicate alliance management at a sensitive moment, saying early warning signs of friction should not be overlooked.