Why withdrawing U.S. troops from Korea risks a two-front war

A recent U.S. Congressional Research Service report, published in June, explored the option of withdrawing 4,500 American troops from South Korea—a potential shift that would bring U.S. force levels on the peninsula below 24,000. While current troop levels already stand at approximately 28,500—among the lowest since the 1953 Armistice and far below Cold War-era peaks—such a reduction would mark the most significant drawdown in decades. Supporters argue this drawdown is necessary to bolster U.S. readiness for a Chinese invasion of Taiwan. But this reallocation of finite Indo-Pacific assets is not just risky—it may prove strategically catastrophic.

As the United States enters an era of dual deterrence fragility, the prospect of simultaneous wars with China over Taiwan and with North Korea on the Korean Peninsula is no longer a distant hypothetical. The Atlantic Council’s recent “Guardian Tiger” simulations, conducted with support from the Defense Threat Reduction Agency, underscore the danger: once engaged in a major conflict with either Beijing or Pyongyang, Washington may find itself unable to deter opportunistic escalation by the other. Far from reinforcing deterrence, reducing U.S. Forces Korea (USFK) could invite the very scenario it seeks to avoid.

The Shifting Strategic Terrain

The logic of the proposed drawdown lies in growing concerns about Taiwan. By 2030, according to U.S. intelligence estimates, China may possess near-peer nuclear capabilities alongside enhanced amphibious, air, and missile forces capable of projecting decisive force across the Taiwan Strait. In parallel, North Korea is deploying a survivable, mobile tactical nuclear arsenal and developing advanced non-nuclear escalatory options, including hypersonic and precision-strike systems.

The Guardian Tiger II scenario began with China launching a multidomain assault on Taiwan, triggering a rapid escalation across the Indo-Pacific. The People’s Liberation Army (PLA) targeted U.S. bases in Japan, launched cyberattacks on allied logistics networks, and threatened missile strikes against USFK if South Korea intervened. Simultaneously, North Korea conducted SRBM demonstrations, cyber intrusions, and a nuclear-capable missile test over the Sea of Japan. Seoul, wary of horizontal escalation, denied USFK involvement in Taiwan—effectively decoupling U.S. deterrence postures and leaving Washington with hard choices and shrinking options.

U.S. strategists often treat North Korea as a secondary actor in a Taiwan contingency. But as Guardian Tiger I demonstrated, Pyongyang sees opportunity in U.S. distraction. In the simulation, a perceived reduction in U.S. resolve—partly due to drawn-out mobilization timelines and restrained early-phase responses—emboldened Kim Jong Un to escalate to chemical, and eventually tactical nuclear, use. A low-yield nuclear strike on a South Korean destroyer forced the U.S. team to contemplate limited nuclear retaliation, risking uncontrolled vertical escalation.

This is not mere theory. North Korea’s 2022 nuclear law codifies pre-delegated use of tactical nuclear weapons in response to existential threats. A visible U.S. drawdown could serve as a green light for miscalculation. As Gen. Curtis Scaparrotti, former commander of U.S. Forces Korea, emphasized, USFK serves as both a stabilizing force and a visible symbol of America’s commitment to South Korea. In this light, the presence of U.S. troops on the peninsula is more than symbolic—it forms the backbone of extended deterrence. Today, that backbone is under threat.

The Taiwan-First Fallacy

Advocates of troop withdrawal argue that deterring Chinese aggression requires massing capabilities—fighters, bombers, long-range fires—closer to the First and Second Island Chains. This logic presumes that Taiwan is the principal theater and that the Korean Peninsula can be held with minimal risk. But the Guardian Tiger simulations expose this logic’s fatal flaw: conflict in one theater is likely to generate escalation in the other, not because of formal coordination between Beijing and Pyongyang, but due to converging opportunism and strategic ambiguity.

In Guardian Tiger II, the decision to reallocate munitions from USFK depots to support operations around Taiwan strained credibility with Seoul and encouraged North Korean brinkmanship. Pyongyang eventually launched an SOF drone attack on U.S. facilities and struck a South Korean airbase with a low-yield nuclear device. Washington was forced into a reactive posture, juggling alliance obligations, limited ISR capacity, and dwindling long-range munitions. This is the Taiwan trap: a zero-sum prioritization that inadvertently invites a two-front war.

Reinforce the Peninsula and the Alliance

Instead of thinning forward presence, Washington should reinforce it. Guardian Tiger recommended updating the Unified Command Plan to establish a new four-star Northeast Asia Command (NEACOM), integrating USFK, U.S. Forces Japan (USFJ), and allied forces under a joint warfighting command. This would enhance lateral coordination, enable synchronized deterrence messaging, and eliminate command bifurcations that slow response and degrade credibility.

Reinforcing USFK with tailored capabilities—such as Terminal High Altitude Area Defense (THAAD) units, maritime ISR assets, and prepositioned precision munitions—would signal resolve to both adversaries. It would also provide Seoul with reassurance that the alliance remains indivisible, especially amid ongoing debates over wartime OPCON transfer and trilateral missile defense interoperability.

Critically, defending Korea does not mean abandoning Taiwan. On the contrary, a strong posture in Korea ensures that deterrence holds there, allowing the U.S. to concentrate force flow and logistical bandwidth in the Taiwan theater without risking a second front. In both simulations, the loss of deterrence in Korea resulted in alliance fissures, force exhaustion, and the looming specter of nuclear escalation. The lesson is clear: maintaining credible deterrence on the peninsula is a prerequisite—not a distraction—from successful deterrence around Taiwan.

Reducing U.S. troops in Korea could also fracture the alliance at a moment when Seoul and Tokyo are beginning to move beyond historical grievances and toward operational convergence. South Korea’s activation of the Republic of Korea Strategic Command (ROKSTRATCOM) and Japan’s creation of a new Joint Operations Command are signs of growing maturity. But both rely on a stable U.S. presence as connective tissue.

As former INDOPACOM Commander Adm. Philip Davidson cautioned in Senate testimony, China’s military strategy increasingly aims to fracture U.S. alliances in the region. He warned that absent a credible U.S. presence and strong partnerships, Beijing would feel emboldened to act. In this context, a troop withdrawal—especially one perceived as prioritizing Taiwan over Korea—would risk doing exactly that.

Deterrence Must Be Distributed, Not Diverted

The Indo-Pacific is entering an age of converging threats and limited bandwidth. Strategic clarity—not artificial prioritization—is now essential. Withdrawing U.S. troops from South Korea to reinforce Taiwan is not a zero-cost reallocation. It is a dangerous gamble that undermines alliance cohesion, degrades deterrence, and increases the odds of a simultaneous two-front war the United States is ill-prepared to fight.

The Guardian Tiger exercises offer a stark warning: deterrence failure in one theater invites disaster in the other. Rather than rob Peter to pay Paul, U.S. policymakers must invest in distributed, integrated, and forward deterrence across Northeast Asia. That begins with keeping U.S. boots—and credibility—on the ground in South Korea.

A recent U.S. Congressional Research Service report, published in June, explored the option of withdrawing 4,500 American troops from South Korea—a potential shift that would bring U.S. force levels on the peninsula below 24,000. While current troop levels already stand at approximately 28,500—among the lowest since the 1953 Armistice and far below Cold War-era peaks—such a reduction would mark the most significant drawdown in decades. Supporters argue this drawdown is necessary to bolster U.S. readiness for a Chinese invasion of Taiwan. But this reallocation of finite Indo-Pacific assets is not just risky—it may prove strategically catastrophic.

As the United States enters an era of dual deterrence fragility, the prospect of simultaneous wars with China over Taiwan and with North Korea on the Korean Peninsula is no longer a distant hypothetical. The Atlantic Council’s recent “Guardian Tiger” simulations, conducted with support from the Defense Threat Reduction Agency, underscore the danger: once engaged in a major conflict with either Beijing or Pyongyang, Washington may find itself unable to deter opportunistic escalation by the other. Far from reinforcing deterrence, reducing U.S. Forces Korea (USFK) could invite the very scenario it seeks to avoid.

The Shifting Strategic Terrain

The logic of the proposed drawdown lies in growing concerns about Taiwan. By 2030, according to U.S. intelligence estimates, China may possess near-peer nuclear capabilities alongside enhanced amphibious, air, and missile forces capable of projecting decisive force across the Taiwan Strait. In parallel, North Korea is deploying a survivable, mobile tactical nuclear arsenal and developing advanced non-nuclear escalatory options, including hypersonic and precision-strike systems.

The Guardian Tiger II scenario began with China launching a multidomain assault on Taiwan, triggering a rapid escalation across the Indo-Pacific. The People’s Liberation Army (PLA) targeted U.S. bases in Japan, launched cyberattacks on allied logistics networks, and threatened missile strikes against USFK if South Korea intervened. Simultaneously, North Korea conducted SRBM demonstrations, cyber intrusions, and a nuclear-capable missile test over the Sea of Japan. Seoul, wary of horizontal escalation, denied USFK involvement in Taiwan—effectively decoupling U.S. deterrence postures and leaving Washington with hard choices and shrinking options.

U.S. strategists often treat North Korea as a secondary actor in a Taiwan contingency. But as Guardian Tiger I demonstrated, Pyongyang sees opportunity in U.S. distraction. In the simulation, a perceived reduction in U.S. resolve—partly due to drawn-out mobilization timelines and restrained early-phase responses—emboldened Kim Jong Un to escalate to chemical, and eventually tactical nuclear, use. A low-yield nuclear strike on a South Korean destroyer forced the U.S. team to contemplate limited nuclear retaliation, risking uncontrolled vertical escalation.

This is not mere theory. North Korea’s 2022 nuclear law codifies pre-delegated use of tactical nuclear weapons in response to existential threats. A visible U.S. drawdown could serve as a green light for miscalculation. As Gen. Curtis Scaparrotti, former commander of U.S. Forces Korea, emphasized, USFK serves as both a stabilizing force and a visible symbol of America’s commitment to South Korea. In this light, the presence of U.S. troops on the peninsula is more than symbolic—it forms the backbone of extended deterrence. Today, that backbone is under threat.

The Taiwan-First Fallacy

Advocates of troop withdrawal argue that deterring Chinese aggression requires massing capabilities—fighters, bombers, long-range fires—closer to the First and Second Island Chains. This logic presumes that Taiwan is the principal theater and that the Korean Peninsula can be held with minimal risk. But the Guardian Tiger simulations expose this logic’s fatal flaw: conflict in one theater is likely to generate escalation in the other, not because of formal coordination between Beijing and Pyongyang, but due to converging opportunism and strategic ambiguity.

In Guardian Tiger II, the decision to reallocate munitions from USFK depots to support operations around Taiwan strained credibility with Seoul and encouraged North Korean brinkmanship. Pyongyang eventually launched an SOF drone attack on U.S. facilities and struck a South Korean airbase with a low-yield nuclear device. Washington was forced into a reactive posture, juggling alliance obligations, limited ISR capacity, and dwindling long-range munitions. This is the Taiwan trap: a zero-sum prioritization that inadvertently invites a two-front war.

Reinforce the Peninsula and the Alliance

Instead of thinning forward presence, Washington should reinforce it. Guardian Tiger recommended updating the Unified Command Plan to establish a new four-star Northeast Asia Command (NEACOM), integrating USFK, U.S. Forces Japan (USFJ), and allied forces under a joint warfighting command. This would enhance lateral coordination, enable synchronized deterrence messaging, and eliminate command bifurcations that slow response and degrade credibility.

Reinforcing USFK with tailored capabilities—such as Terminal High Altitude Area Defense (THAAD) units, maritime ISR assets, and prepositioned precision munitions—would signal resolve to both adversaries. It would also provide Seoul with reassurance that the alliance remains indivisible, especially amid ongoing debates over wartime OPCON transfer and trilateral missile defense interoperability.

Critically, defending Korea does not mean abandoning Taiwan. On the contrary, a strong posture in Korea ensures that deterrence holds there, allowing the U.S. to concentrate force flow and logistical bandwidth in the Taiwan theater without risking a second front. In both simulations, the loss of deterrence in Korea resulted in alliance fissures, force exhaustion, and the looming specter of nuclear escalation. The lesson is clear: maintaining credible deterrence on the peninsula is a prerequisite—not a distraction—from successful deterrence around Taiwan.

Reducing U.S. troops in Korea could also fracture the alliance at a moment when Seoul and Tokyo are beginning to move beyond historical grievances and toward operational convergence. South Korea’s activation of the Republic of Korea Strategic Command (ROKSTRATCOM) and Japan’s creation of a new Joint Operations Command are signs of growing maturity. But both rely on a stable U.S. presence as connective tissue.

As former INDOPACOM Commander Adm. Philip Davidson cautioned in Senate testimony, China’s military strategy increasingly aims to fracture U.S. alliances in the region. He warned that absent a credible U.S. presence and strong partnerships, Beijing would feel emboldened to act. In this context, a troop withdrawal—especially one perceived as prioritizing Taiwan over Korea—would risk doing exactly that.

Deterrence Must Be Distributed, Not Diverted

The Indo-Pacific is entering an age of converging threats and limited bandwidth. Strategic clarity—not artificial prioritization—is now essential. Withdrawing U.S. troops from South Korea to reinforce Taiwan is not a zero-cost reallocation. It is a dangerous gamble that undermines alliance cohesion, degrades deterrence, and increases the odds of a simultaneous two-front war the United States is ill-prepared to fight.

The Guardian Tiger exercises offer a stark warning: deterrence failure in one theater invites disaster in the other. Rather than rob Peter to pay Paul, U.S. policymakers must invest in distributed, integrated, and forward deterrence across Northeast Asia. That begins with keeping U.S. boots—and credibility—on the ground in South Korea.

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Dr. Ju Hyung Kim, president of the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly, is currently adapting his doctoral dissertation, “Japan’s Security Contribution to South Korea, 1950 to 2023,” into a book.