Strategic flexibility and Korea’s return to the frontlines of conflict

Strategic flexibility—the U.S. doctrine that deems forward-deployed forces, including those in South Korea, ready to respond to crises anywhere in the region—is knitting the Korean and Taiwan theatres together once again.

In the early Cold War, the fates of Taiwan and the Korean Peninsula were not seen as distinct. They were treated as two nodes in a single strategic contest between the U.S.-led bloc and the Communist powers of China and the Soviet Union. U.S. forces stationed in South Korea and the Taiwan Strait patrolled overlapping threat environments, responding to crises in either theatre with a regional logic of containment.

By the 1990s, that logic had shifted. The Cold War was declared over, and the strategic linkage between Korea and Taiwan was decoupled. South Korea focused inward—its military prioritized defense against the North, and its diplomacy sought regional stability, not expeditionary entanglement.

That separation between Korea and Taiwan is now being undone.

For South Korea, the decision to allow these forces to be used beyond the peninsula was finalized under the Yoon Administration, but its implications are only now being more closely considered. Advisors coming into power under the Lee Administration are not unquestioningly dedicated to the concept. Some are vehemently opposed.

On paper, it gives Washington agility. In practice, it risks transforming South Korea from a stable peninsula guarding its own security into a forward operating base for a larger U.S.-China confrontation.

The consequences of this shift are not abstract. South Korea’s involvement in America’s regional planning is no longer limited to deterring North Korean aggression.

With strategic flexibility, U.S. Forces Korea (USFK) could be rapidly deployed to assist in a Taiwan contingency—drawing South Korea into a war it did not provoke, over an issue it did not choose.

This isn’t a hypothetical. U.S. Indo-Pacific Command has been quietly integrating its contingency planning across theatres, and war games involving Taiwan scenarios increasingly assume that U.S. assets in Korea would be mobilized early. These include logistics hubs, airlift routes, and even U.S. missile defense and ISR assets currently stationed south of Seoul.

It’s important to note, this is not a Trump Administration agenda. It is an agenda that has been continuing unabated since the post-Cold War period. The strategy has steadily advanced across U.S. administrations, regardless of party. Under both Democratic and Republican leadership, the Pentagon and Indo-Pacific Command have pursued greater integration of U.S. forces in the region, including those in Korea, into wider contingency planning.

The logic is institutional, not political: military planners seek to maximize flexibility and readiness across theatres. As a result, the weaving of USFK into Taiwan-related scenarios has continued through the Obama, Trump, and Biden years—not as a product of partisan policy, but as a reflection of enduring U.S. strategic priorities in the face of a rising Chinese military threat.

For South Korea, this means that the pressure to be indirectly drawn into a Taiwan conflict will persist, no matter who occupies the White House.

South Korea, by accepting this logic, is effectively placing itself back on the frontline of great power conflict. The irony is striking: for decades, South Korea tried to regionalize and de-escalate its security outlook—recasting itself as a middle power focused on diplomacy, development, and trade.

Now, with little public debate and under the guise of alliance modernization, it is sliding into the role of a frontline state in a brewing U.S.-China conflict.

This exposes South Korea to significant risk. China has already hinted that South Korea’s alignment on Taiwan will shape the future of bilateral relations. In a Taiwan conflict, Beijing will treat U.S. bases in South Korea as legitimate targets—regardless of whether they are used to stage operations.

Seoul might protest that its role is defensive, but war has no time for nuance. The moment U.S. aircraft take off from Osan or USFK assets are rerouted to a Taiwan mission, South Korea becomes part of the war.

Worse, strategic flexibility undermines South Korea’s ability to define its own interests. It allows Washington to set the terms of engagement, while Seoul absorbs the fallout. If U.S. forces launch operations from Korea without Seoul’s consent, the alliance is hollow. If Seoul consents, it becomes a belligerent. In either case, autonomy is compromised.

This is a far cry from the strategic logic of the post-Cold War period, when Korea’s security was managed primarily on its own terms, through deterrence and gradual inter-Korean diplomacy. Back then, the separation of the Taiwan and Korea theatres was a reflection of reality: one was about cross-strait tension, the other about the armistice on the peninsula. Now, that separation is being erased not because of necessity, but because of strategic ambition in Washington.

Policymakers in Seoul are asking: whose war is this? And are we prepared for what participation means? Advisors are listening.

The logic of strategic flexibility serves American goals. It helps balance Chinese power, reinforces U.S. regional deterrence, and provides operational depth. But what does it give South Korea?

More exposure, more entrapment risk, and more strain on already fraught ties with Beijing. All while doing little to actually reduce the threat from North Korea—still the only actor that can reliably turn Seoul into a warzone within minutes.

The United States can afford to be flexible. It has distance, resources, and options. South Korea does not.

Its capital lies within range of thousands of artillery pieces. Its economy depends on Chinese markets. Its people have no appetite for war over Taiwan. And yet, by hosting U.S. forces without clear limitations, and by refusing to draw red lines on operational use, it is giving Washington a blank cheque.

Strategic flexibility is not an abstract principle. It is a doctrine of war planning. If South Korea does not reclaim its voice in that planning, it will find itself a participant in a war it did not start, over a dispute it cannot shape, and with consequences it will suffer far more than those who planned it.

The frontline is shifting again—and South Korea was walking toward it with its eyes wide shut. Some in the Lee Administration are not.