Revisiting Yoon’s Martial Law Decree: A Wake-Up Call
Korean President Yoon Suk-yeol’s martial law decree in December of last year was a shock to South Koreans, Americans, and the entire world. How did this plot evade so many intelligence radars?
The leak of classified U.S. documents in April 2023 exposed yet another instance of American intelligence eavesdropping on its allies. Among the trove of leaked materials, three documents pertained to South Korea, two of which were classified as Special Intelligence (SI), a designation that confirms they were derived from intercepted communications.
This revelation reignited longstanding suspicions that the United States has been surveilling South Korea. From the Park Chung-hee era to the Snowden disclosures revealing National Security Agency (NSA) wiretaps on South Korean embassies and UN missions, such practices are hardly unprecedented. Despite this history of surveillance, U.S. intelligence agencies failed to foresee South Korean President Yoon Suk-yeol’s plan for emergency martial law in December of last year.
The recent revelation that the outgoing U.S. ambassador to South Korea expressed dismay over the martial law plan underscores the gravity of this intelligence failure.
Left In The Dark
These intelligence failures render policymakers scrambling for critical information, leading to miscalculations and decisions that ultimately undermine national security interests for both the U.S. and South Korea. Such failures are rarely the result of mere negligence, rather they are deeply rooted in cognitive biases, structural limitations, and institutionalized modes of intelligence collection and analysis.
From the Central Intelligence Agency’s (CIA) misjudgment of Soviet intentions during the Cold War to the erroneous belief in Iraq’s weapons of mass destruction, intelligence failures often stem not from a lack of information but from misinterpretation of available signals. What happened in South Korea is another case in point.
Warnings about Yoon’s potential martial law declaration had surfaced from opposition parties long before December, yet there is no indication that U.S. intelligence agencies in Seoul detected, or attempted to prevent, the unfolding crisis.
How could the vast intelligence apparatus, deeply embedded within South Korea’s national security network, fail to detect such a dangerous coup attempt in the making? What fundamental flaws in intelligence gathering and analysis does this failure expose?
The issue was likely not an absence of signals but a failure to assess their significance. Intelligence agencies operate under overwhelming information constraints, forced to sift through signals and noise while prioritizing emerging threats.
How Was This Missed?
Historically, the U.S. intelligence network in South Korea has focused on military and diplomatic developments concerning North Korea and China. Surveillance efforts have prioritized missile tests, nuclear threats, and diplomatic negotiations. In this framework, domestic political maneuvering in a post-democratization South Korea, especially covert plans formulated within the president’s inner circle, did not align with existing intelligence priorities.
The court proceedings that followed exposed the extent to which the martial law master plan had been tightly guarded within a small group of key figures.
Intelligence failures often become evident only in hindsight. Analysts may well have noticed an accumulation of seemingly minor red flags: military orders issued at odd hours, shifts in Yoon’s rhetoric, or quiet legal reviews of emergency powers, but without an intelligence framework that accounted for South Korea’s internal political dynamics, these signals would have been dismissed as background noise.
This reflects a classic case of expectation bias, a persistent issue in intelligence assessments. Analysts tend to expect events to conform to established patterns, and when faced with evidence that deviates from these patterns, they are more likely to disregard it as an anomaly rather than a warning.
Technical intelligence collection is not always reliable. Sophisticated encryption, restricted communications, and handwritten notes exchanged during face-to-face meetings reduce the effectiveness of signals intelligence (SIGINT), imagery intelligence (IMINT), communications intelligence (COMMINT), and electronic intelligence (ELINT).
The South Korean government has also strengthened its cybersecurity measures to counter foreign eavesdropping. Ultimately, intelligence collection is only as effective as the extent to which a target, or even an ally, allows access. If Yoon’s plot exercised tight operational security, traditional surveillance methods would have struggled to detect the plot.
A second factor contributing to this intelligence failure is the shifting strategic priorities of the outgoing Biden administration. As Washington navigated the complexities of administration transition, the White House was preoccupied with crises in Ukraine, Taiwan, and the Middle East.
South Korea’s internal political volatility was likely deemed a lower priority, the assumption being that allies remain stable and predictable has long contributed to intelligence failures. Policymakers and intelligence analysts alike tend to overestimate the resilience of democratic institutions and underestimate early warning signs of systemic breakdowns. South Korea may have been yet another case of misplaced confidence.
Taking Stability For Granted
The leadership transition within the U.S. intelligence community may have further exacerbated the problem, given that political appointees at the CIA and NSA are routinely replaced with each new administration, leading to shifts in intelligence priorities. If discussions of martial law in South Korea took place during such a transitional period, intelligence warnings may have been deprioritized or lost amid the bureaucratic reshuffling.
Furthermore, intelligence assessments must pass through multiple layers of review before reaching policymakers, increasing the likelihood that critical warnings are diluted or dismissed.
The attempted martial law declaration by President Yoon highlights the need for intelligence frameworks to be more adaptable and capable of reassessing entrenched assumptions, essentially because positive impressions from personal interactions with counterparts will lead a decision-maker to view their counterpart in a more friendly way.
Intelligence analysts in Seoul and Washington, humbled by this intelligence failure, may now realize that monitoring external threats is not enough; they must also scrutinize the political dynamics of allied nations. Washington’s longstanding assumption that South Korea is a stable actor operating within predictable boundaries must be fundamentally reevaluated.
Improving the intelligence batting average will require greater flexibility in recognizing and acting on unexpected threats.
As the complexity of U.S.-ROK relations deepens, the contours of this alliance will soon become clearer. There was a time when American power was both a burden and a source of resilience for South Korea.
For decades, Washington assumed that its closest allies could be trusted to operate within predictable norms. However, as this intelligence failure shows, even familiar allies can wield the ax.
The chances of the blade flying off the handle is low, but never at zero.
Byong-Chul Lee is an Assistant Professor at Kyungnam University’s Institute for Far Eastern Studies (IFES) in Seoul, South Korea. His research interests include North Korean denuclearization, nuclear non-proliferation, and policies on ROK-US relations. Before joining the IFES, Dr. Lee worked as an aide to the Presidential Senior Secretary for Foreign and National Security Affairs and served as a foreign and national security policy planning staff member at the Presidential Office of South Korea from 1993 to 1999. He also served as a special aide and policy planning secretary to the Speaker of the National Assembly from 2015 to 2016. His op-eds and comments have appeared in The New York Times, 38North, Bulletin of the Atomic Scientists, YaleGlobal, Project Syndicate, and The South China Morning Post, among other publications.
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