Why is the Yellow Sea so important?

in

This is the script for my video posted on August 4, 2026. Watch it on TikTok.

The Yellow Sea is one of the most strategically sensitive bodies of water in the world. It's bordered by China, North Korea, and South Korea, and the United States gets pulled in by treaty. The Yellow Sea’s inner gulf, the Bohai, reaches to within about 150 kilometers of Beijing. So how exactly does the Yellow Sea shape geopolitics?

The Yellow Sea has decided the fate of empires. In 1894 and 1895, Japan annihilated China's Beiyang Fleet here and ended Chinese naval power in Asia for a century.

Ten years later, Japan and Russia fought the Battle of the Yellow Sea over the approaches to the same coastline. And in 1950, MacArthur's landing at Incheon, on the Yellow Sea, reversed the Korean War in about two weeks.

China remembers all of this vividly and has been excavating those sunken Beiyang warships since 2014, teaching them as a national humiliation.

The Yellow Sea, excluding the Bohai Sea which is considered Chinese internal waters, extends about 960km from north to south and 700km from east to west.

It's a lot of water, but the average depth is only around 44 meters, and even at its deepest, in a trough that runs north to south along the Korean side, it's only about 150 meters.

This shallowness, combined with turbidity and low salinity, makes sonar much less reliable. And that cuts both ways. It's bad water for large nuclear submarines, but it's close to ideal for small, quiet diesel and midget subs, which are extremely difficult to find. This will be important later.

Typically, a country’s Exclusive Economic Zone, or EEZ, covers 200nm from its coastline, but the Yellow Sea is too narrow for South Korea or China to fully claim that area. They are guaranteed to overlap, and this is the source of the dispute underlying the entire environment.

South Korea favors a median or equidistance line, but China has historically argued that other factors like the continental shelf, coastline length, and population should push the boundary east.

They've negotiated exclusive national fishing zones and a jointly managed Provisional Measures Zone, or PMZ. The agreement that entered force in 2001 permits only fishing and navigation inside that zone, which means fixed structures arguably aren't allowed at all. Talks on a permanent boundary stalled for years, and the two sides still haven't agreed on one.

Nonetheless, China has been placing buoys and salmon aquaculture cages inside the PMZ since 2018. In 2024 it added a repurposed oil rig as a central hub, with housing, a helipad, and an operations center, which raised obvious questions about what else a platform like that could support. In 2025, South Korean intelligence revealed the existence of a steel structure over 50 meters across and 50 meters tall, with more reportedly planned.

China's answer is simple: these are fish farms, and the 2001 agreement never mentions aquaculture, so nothing forbids them. And to be fair, the analysts tracking these platforms by satellite mostly agree they do appear to be genuinely farming fish. The concern was never what they are today. It's the precedent they establish.

A South Korean research vessel attempted to survey the structures, but they were blocked by the Chinese coast guard. This has been growing more common and is widely perceived as a Chinese attempt to exert de facto sovereignty over the area. In May 2025 they even declared temporary closure zones in the shared PMZ for China’s aircraft carrier, the Fujian, to conduct exercises. Chinese warships entered waters under South Korean jurisdiction more than 330 times in 2024 alone, up from about 110 times in 2017.

Then in January 2026 the picture shifted. At a summit in Beijing, the Chinese and South Korean presidents agreed to restart negotiations on a formal maritime boundary, the first such talks in roughly seven years, and China agreed to move the oil rig. By the end of that month it was relocated to a shipyard at Weihai. But the cages and buoys stayed. So the structure that generated the headlines is gone, and the presence it established is not.

North Korea creates a second set of problems here. The armistice that ended the Korean War in 1953 delimited the military demarcation line on land that we now call the DMZ, but this did not extend a boundary into the Yellow Sea.

The UN Command drew its own line instead, called the Northern Limit Line. Declassified American documents have said plainly that it has no basis in international law, but South Korea argues that seventy years of practice have made it the de facto border regardless. North Korea has been working within that gap.

There have been several naval clashes since 1999, but 2010 was the deadliest year by far. That March, a 1200 ton South Korean corvette sank near the Northern Limit Line, killing 46 of its 104 sailors. An international investigation concluded a North Korean midget submarine had gone undetected and torpedoed it, demonstrating the shallow water problem in practice.

Friction often spikes in early summer, when blue crab season pulls fishing fleets from all three countries up against the Northern Limit Line, where the ambiguity tends to generate conflict over territory.

North Korea also uses these waters to evade sanctions, moving coal out of Nampo and taking on oil through ship-to-ship transfers, though a lot of that transfer activity happens further south in the East China Sea.

The northern Yellow Sea and the Bohai are the PLA Navy's protected waters for sea trials and exercises. Dalian is a major yard for surface warships and for aircraft carriers. It refitted the Liaoning, built the Shandong, and is building the next carrier now. And the Bohai shipyard at Huludao has been China's principal nuclear submarine production facility for decades.

China is extremely sensitive about this water because of what sits behind it, and that became obvious in 2010, when the US and South Korea exercised the USS George Washington carrier strike group in the Yellow Sea. China objected loudly and repeatedly. The carrier's air wing, and the cruise missiles aboard its escort ships, could reach well inland even from far off the coast, and this is one source of China’s efforts to control the Yellow Sea more broadly.

China, North Korea, South Korea, and the United States all have direct security stakes in this one sea, and three of them are nuclear-armed. Which means something that would be a minor military or diplomatic incident anywhere else in the world carries the risk of catastrophic escalation.

An incident between China and South Korea could implicate the US, but this is unfortunately ambiguous like so many aspects of Korean geopolitical dynamics. The 1953 mutual defense treaty covers an armed attack in the Pacific area on territories under each party's administrative control, and the US Senate narrowed it further to territory the US recognizes as lawfully under South Korean control. Even then, the US commits only to act in accordance with its constitutional processes, meaning they get to choose how and if they will respond.

But look at what that leaves out. A coast guard cutter blocking a survey ship is not an armed attack. A buoy isn’t a border. A fish farm is not an invasion. China can slowly shift expectations to get what they want. That's the entire logic of gray zone competition, and the Yellow Sea is a perfect example of it.

Keep reading

I’m writing a book called Groundwork about the buried history beneath geopolitics. Join the waitlist to hear when it has a publisher, a cover, and a release date.