Get audio access with any FP subscription. Subscribe Now ALREADY AN FP SUBSCRIBER? LOGIN

Get audio access with any FP subscription.

ALREADY AN FP SUBSCRIBER? LOGIN

On March 27, China began blocking off five airspace zones over roughly 340 miles of the disputed Yellow Sea and East China Sea, including waters where U.S. and South Korean aircraft regularly operate. China’s Aeronautical Information Service, the issuer of the notice, offered no altitude ceiling and no explanation for the 40-day closure, which is set to expire on May 6.

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.

On March 27, China began blocking off five airspace zones over roughly 340 miles of the disputed Yellow Sea and East China Sea, including waters where U.S. and South Korean aircraft regularly operate. China’s Aeronautical Information Service, the issuer of the notice, offered no altitude ceiling and no explanation for the 40-day closure, which is set to expire on May 6.

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.

!function(e,n,i,s){var d="InfogramEmbeds";var........

© Foreign Policy