The United States’ Korea Strategy Is Working Against Itself

This incident is part of a broader pattern of Chinese gray-zone pressure—military activity calibrated to coerce without crossing the threshold of armed conflict—along South Korea’s air and maritime boundaries, following the playbook that China has run against the Philippines in the South China Sea, against Japan near the Senkaku Islands, and against Australia after Chinese warships conducted live-fire exercises in the Tasman Sea. But while those campaigns drew headlines, Beijing’s pressure on Seoul largely has not.

Newly consolidated data from South Korea’s Ministry of National Defense, drawn from National Assembly disclosures and reproduced across multiple domestic sources, shows a sharp rise in Chinese incursions into sensitive zones since 2021. The pattern closely tracks U.S.-South Korea alliance decisions, easing when South Korea accommodates China, intensifying when it aligns with the United States.

This suggests that as the Trump administration seeks to shift alliance burdens onto South Korea, it is also multiplying the burdens that its ally must bear by drawing Seoul into its rivalry with Beijing. This has real consequences for South Korea’s military and its ability to lead against North Korea—and ultimately, Washington’s hopes of pivoting toward China.

The evidence emerges from two boundary zones. The Korea Air Defense Identification Zone (KADIZ) is the airspace within which South Korea requires aircraft to identify themselves. It is not sovereign territory, but unauthorized entry triggers a military response. China’s own air defense identification zone partially overlaps with this—a friction that Beijing exploits to claim plausible deniability. The Provisional Measures Zone (PMZ) is the de facto maritime boundary in the Yellow Sea, spanning 150,000 square miles. It is a flash point over what Beijing describes as “deep-sea fishery aquaculture facilities” but which Seoul views as encroachments.

From 2016 to 2020, Chinese military aircraft entered KADIZ between 50 times and 140 times annually. Early on, as Beijing and Seoul deepened their economic and diplomatic partnership, incursions were low. But as the bilateral relationship deteriorated, that calculus changed. Incidents spiked in 2018, moderated through 2019 and 2020, then surged again after 2021—each shift mirroring a change in Seoul’s alignment with Washington.

China initially responded with economic retaliation; by late 2017, diplomatic signaling had eased some of that pressure, but the underlying friction remained. Relations stabilized during 2019 and 2020 as South Korea’s president at the time, Moon Jae-in, worked to maintain close ties with both Washington and Beijing, nurturing a diplomatic environment for U.S. President Donald Trump’s talks with North Korea.

But that period of relative calm did not survive the breakdown of those talks and the change of administration in Washington. Former U.S. President Joe Biden’s administration began pulling the alliance away from peninsula-focused deterrence and toward a broader Indo-Pacific posture aimed at countering Beijing. At the May 2021 Biden-Moon summit, Seoul acknowledged for the first time “the importance of preserving peace and stability in the Taiwan Strait” and agreed to align South Korean policy with Washington’s Indo-Pacific framework. Moon continued to pursue accommodation with Beijing, but Washington was steadily integrating South Korea—and the alliance itself—into its China strategy.

Beijing’s response was calibrated. It applied military pressure through the KADIZ and Yellow Sea while keeping economic and diplomatic channels open, signaling displeasure without escalating to full-scale retaliation. Maritime incursions near the PMZ, tracked systematically from 2021, totaled 220 incidents that year. As alignment with Washington deepened, those numbers climbed. Combined KADIZ and PMZ incidents reached 490 in 2023—a record—before falling slightly to 420 in 2024. Some of this may reflect improved South Korean monitoring, but the direction is clear.

The surge tracks alliance decisions closely. When former South Korean President Yoon Suk-yeol took office in 2022 and pursued closer ties with Japan, deepened NATO engagement, and embraced Washington’s Indo-Pacific framework, Beijing took notice—though not immediately.

Incursions were relatively moderate in Yoon’s first year, suggesting that Beijing gave the new administration a window before responding more forcefully. The diplomatic nadir came in April 2023, when Yoon’s remarks on Taiwan triggered a Chinese diplomatic firestorm, and Beijing’s ambassador warned, “Those who bet on China’s loss will surely regret their decision.” The 2023 incursion peak coincided with that period, leaving South Korea to absorb roughly one to two incidents per day. The Camp David trilateral summit in August 2023, which institutionalized the U.S.-Japan-Korea security relationship in ways that Beijing read as explicitly anti-China, appears to have been another major trigger.

As the most recent Yellow Sea closure shows, this doesn’t bode well for the alliance under the Trump administration, which has doubled down on demands that put South Korea in China’s crosshairs.

In November, the United States and South Korea affirmed that Seoul “will assume the leading role in the defense of the Korean Peninsula.” Hours later, in the same building, U.S. Defense Secretary Pete Hegseth added that “flexibility for regional contingencies is something we would take a look at”—a reference to reorienting U.S. Forces Korea toward China, including a potential conflict over Taiwan. Washington did not appear to understand the tension between these two requirements and that demanding one necessarily makes the other more difficult.

Washington’s strategic logic is straightforward enough. It wants Seoul to invest in the capabilities and posture needed to manage the North Korean threat while the United States provides the nuclear backstop and reorients toward China. The 2026 U.S. National Defense Strategy is unambiguous: “South Korea is capable of taking primary responsibility for deterring North Korea with … limited U.S. support,” and “this shift in the balance of responsibility is consistent with America’s interest in updating U.S. force posture on the Korean Peninsula.”

By conventional metrics, Seoul has been slowly delivering. Defense spending is rising: South Korean President Lee Jae-myung requested an 8.2 percent increase for 2026, explicitly framed as reducing reliance on the United States. Both sides have agreed to certify a key milestone in transferring wartime operational control by the end of this year. Seoul has also pledged $350 billion in U.S. investment and $25 billion in military equipment purchases by 2030. On paper, the alliance is moving in the direction that Washington wants.

But Washington’s other demands are undercutting this goal. In February, U.S. F-16 fighters launched from Osan Air Base and approached China’s air defense identification zone over the Yellow Sea; Chinese fighters scrambled in response. South Korean defense officials called the U.S. Forces Korea commander to protest: Washington had used assets based in South Korea for a China-facing operation without consulting the ally hosting them, leaving Seoul to manage a confrontation that it had not authorized.

The embrace of strategic flexibility was Seoul’s choice as much as Washington’s, but the costs of this strategy fall on South Korea alone. And what Washington does not pay for, it has little reason to change. Each time that Seoul aligns publicly with Washington on China-related issues—a statement on Taiwan, a reorientation of U.S. Forces Korea, a mission flown from Korean soil—Beijing responds. At a tempo of nearly 500 incursions annually, South Korea’s air force and navy are running a continuous interception cycle that degrades readiness, strains maintenance, and pulls attention away from the North Korean mission.

The division of labor that Washington is asking for depends on a capable, committed, and unencumbered ally; this cannot be delivered by a country preoccupied with managing Chinese coercion.

Though Washington has created this problem, it can also correct it.

The first step is getting out of South Korea’s way. True burden-shifting means giving Seoul genuine latitude to manage its relationship with Beijing. Not every South Korean hedge represents a failure of resolve or a drift from the alliance. If Seoul can manage Chinese pressure through back-channel diplomacy, calibrated public statements, and bilateral crisis mechanisms, then it can focus on North Korea without having to worry about Chinese retaliation.

This will not eliminate Chinese gray-zone pressure entirely. Beijing views any strengthening of the U.S.-South Korea alliance as a threat to the regional balance, regardless of whether it is directed at North Korea or China. But an alliance focused on peninsula deterrence invites a different and more limited Chinese response than if Seoul were publicly aligned with Washington’s Taiwan policy or hosted operations aimed at Beijing. The goal is not to remove Chinese pressure—that is beyond Washington’s power to offer—but to stop generating more of it than the mission requires.

Washington should also push Seoul to strengthen its deterrence capabilities in two complementary ways. The first is denial: missile defense, cheap drones, better surveillance and early warning, and more mobile and dispersed strike assets. The signal to Pyongyang should be that any first strike will fail to neutralize South Korea’s ability to respond. The second is punishment. Seoul should quietly build retaliatory strike capabilities aligned with the “Korea Massive Punishment and Retaliation” plan, selectively revealing enough to reinforce deterrence. Seoul is investing in both areas, but critical gaps remain. Its drone fleet is largely aspirational, and its ability to detect and intercept cheap drones—the kind that North Korea is already mass-producing—is limited.

Correcting the strategic incoherence will reduce Chinese gray-zone behavior, but it will not eliminate it or the ensuing risks. There are several China-South Korea contact lines for KADIZ and PMZ incidents, but Chinese counterparts answer them inconsistently. Washington should make functioning military hotlines a priority in its own diplomacy with Beijing rather than leaving Seoul to solve it alone.

The United States and South Korea also need agreed procedures for identifying, communicating, and standing down incidents—analogous to the incident-at-sea agreement that kept U.S.-Soviet military encounters from spiraling during the Cold War. With no agreed framework, the hundreds of incursions annually are an accident waiting to happen.

In the meantime, Beijing is not waiting for Washington to resolve the contradiction. Washington can either ask Seoul to lead on North Korea, or it can continue pulling Seoul into its rivalry with Beijing. Trying to do both is a setup for failure to do either—and the longer that Washington avoids that strategic reality, the more that it undermines its own agenda.