From South China Sea to the Yellow Sea: China’s Gray Zone Tactics and Strategic Lessons for South Korea

This thesis examines China’s maritime gray zone tactics and their implications for South Korea, focusing on the Yellow Sea. Gray zone tactics—coercive measures below the threshold of armed conflict—include the use of maritime militias, coast guard patrols, artificial structures, and economic leverage. These actions have reshaped the security environment in the South and East China Seas and are now extending northward, challenging South Korea’s maritime sovereignty and stability. Employing a comparative case study method, the thesis analyzes responses by the Philippines, Japan, and Vietnam through the DIME (Diplomatic, Informational, Military, Economic) framework. The Philippines has emphasized legal arbitration and informational campaigns, gaining international support but limited enforcement. Japan relies on persistent patrols and alliance coordination, constraining Chinese actions but at high operational cost. Vietnam pursues a hedging strategy, balancing militarized outposts with economic engagement, maintaining stability yet facing sustained pressure. The analysis highlights lessons for South Korea: reliance on the U.S. alliance is insufficient, transparency and media strategies can bolster deterrence, and selective military and economic measures strengthen resilience. The study concludes that the Yellow Sea is emerging as a new arena of gray zone competition, requiring Seoul to adopt a proactive, whole-of-government strategy that safeguards sovereignty while contributing to regional stability.