Yoon Suk Yeols legacy threatens to erode US-South Korea alliance

First published by Pacific Forum‘s The Pilot: Indo-Pacific Policy Briefs, this article is republished with permission.

Last week, former South Korean President Yoon Suk Yeol (2022-25)receiveda life sentence for leading an insurrection in connection to his aborted martial law declaration in December 2024.

A few days later, it came to light that South Korea hadobjectedto a proposed trilateral air exercise with the United States and Japan on February 16 and 18,citingconcerns of being dragged into the US-China rivalry, leaving the other two countries to carry out those exercises bilaterally.

These events are not unrelated.

Given his very narrow 2022 election and legislative minority, Yoon was always going to struggle at building a legacy, in comparison with his conservative predecessors as South Korean president.

Unlike Park Chung-hee (1961-79), he could not use his military command to shepherd the country through an era of rapid economic development.

Unlike former General Roh Tae-woo (1988-93), he could not use the presidency in the waning days of the Cold War to normalize relations with former Communist Bloc members and lead South Korea into the UN.

Unlike Kim Young-sam (1993-98), he could not use the status of the first civilian leader following the military rule period to solidify the country’s democratic transition, firmly asserting civilian control over the military and campaigning against the corruption of his predecessors.

One could say that Yoon – who faced an adversarial, even obstructionist, National Assembly throughout his term – seized the one chance he had at establishing a long-term legacy for the country: his 2022 decision to break the deadlock with Japan by traveling to Tokyo and meeting then-Prime Minister Fumio Kishida.

That shift has faced much domestic derision since, with Yoon accused of everything fromsubmissivenessto outrightbetrayalof the national interest. Had his interlocutor not been the mild-mannered Kishida but the farmore hatedShinzo Abe, the backlash would have been even worse.

Still, previous conservative presidentsattemptedrapprochement with Japanese leaders and had their workundoneonce the progressive opposition came to power, making questionable the longevity of Yoon’s quest.

Four years later, it appears that Yoon’s gamble benefited Korea – if not Yoon himself. His successor, progressive President Lee Jae-myung, has upheld bilateral cooperation. And even Japan’s selection of the staunch nationalist (and protégé of Abe) Sanae Takaichi has not causedbilateral ties to fray. This could have been Yoon’s legacy.

It very well might have been his legacy, had Yoon finished his five-year term without acting rashly. That would have meant enduring, until May 2027,consistent oppositionfrom the Democratic Party of Korea and its legislative majority, as well as the legal scrutiny of his andhis wife’s and his associates’ dealings in government. Based on thefatesof hispredecessors, legal scrutiny would have followed him after leaving office.

Yet, instead of positioning himself as a tragic figure who made personal sacrifices for his country, Yoon chose to declare martial law and attempt what’s called in Spanish an autogolpe – a self-coup or coup from the top – on December 3, 2024.

His supporters have sought to justify this act – not only with reference to thehistorical precedentPark Chung-hee established in May 1961 (followed by Chun Doo-hwan inDecember 1979) but also by citing the obstructionist tendencies of his opponents in the legislature, and theallegations(some of whicharetrue) of Beijing’s mounting malign influence in the country.

However, as the Constitutional Courtnotedlast year in its decision upholding Yoon’s impeachment, there was no legal basis for his declaration. There was no imminent security rationale. Among the powers of the president of the Republic of Korea is the right to declare martial law – but Yoon’s methods were not consistent with those outlined legally.

Information we have learned about Yoon’s plans foropposition politiciansandthe presshave brought back deeply unpleasant memories to those who remember the barriers thrown up against the democratic movements of the 1980s and earlier.

Yoon is not related to Park Chung-hee. Heprosecuted Park’s daughterfor corruption. And he did not have Lee Myung-bak’stiesto the country’schaebolconglomerate class. With none of those entangling domestic alliances he could have represented a clean break for a conservative movement in a democratic era.

The movement needed fresh voices in support of fiscal conservatism, constitutionalism and democratic coalition-building with Washington and Tokyo against Beijing and its partners.

Instead, pro-US voices on the Korean right – confronted with reports of how Yoon wanted Democratic Party of Korea politicians dragged out of the National Assembly and wanted press freedom stifled – have yet another reputational black mark to live down.

Lee Jae-myung had mostly reaffirmed the value of the alliance with the United States and cooperation maintenance with Japan since taking office last summer.

But his apparentdefault position– of pursuing harmony in Sino-Korean relations and promotingindependencefrom US security guarantees – revealed itself in the ROK’s refusal to join the air exercise, citing an unwillingness to anger China.

This will have ramifications if the United States seeks commitments to help deter a Taiwan contingency, call out Beijing’s predatory behavior in the South China Sea or build economic resilience through regional coordination.

Indeed, unless the PRC reverts to the sort of behavior that drove so many of its neighbors into the arms of the United States between 2017 and 2022, or Washington suddenly becomes a lot more proactive in its use of soft power below the Demilitarized Zone, developments suggest an erosion of US influence in the Republic of Korea, to China’s benefit.

Good bilateral relations with Japan seem certain to be tested once Lee’s conciliatory approach to the PRC clashes with Takaichi’s more outspoken stance.

The primary legacy of Yoon’s martial law declaration is not his own life sentence. Like most past South Korean presidents who have faced legal trouble, he almost certainly will be pardoned eventually.

The real tragedy may be in erosion in the US-ROK alliance – something that Yoon, with more patience and forbearance, might have avoided.

Rob York (rob@pacforum.org) is director for regional affairs at Pacific Forum. He earned his PhD in Korean history in 2023.