Here's What You Need to Remember: The South China Sea isn't anyone's sea. It belongs to the whole world. But the country that would suffer most from its closure in time of war would be China.

Who owns the high seas? The conventional answer is: no one and everyone.

Coastal states exercise sovereignty over territorial waters that normally extend 12 nautical miles from their shorelines. They also have the right to exploit undersea resources like oil and gas in exclusive economic zones that extend out 200 nautical miles. Economics rights can even be extended further to incorporate the entire continental shelf before the seabed falls off into a deep ocean basin.

These lawyerly definitions are contentious enough in their own terms, but they are next to meaningless when it comes to security strategy. That's because legal terms like "sovereignty" and "rights" depend on possession, and it is notoriously difficult to possess the seas. If possession really is nine-tenths of the law, that explains why the Law of the Seas is so difficult to enforce. Turn your back for one minute, and you may find your former maritime possessions already in someone else's hands.

The Chinese understand this better than anyone, which is why they have been so successful (if that's the word for it) at expanding their possessions in the South China Sea. Other countries may deny China's legal claims, or even fun freedom of navigation operations close to Chinese-held artificial islands, but even the United States doesn't dare send Marines ashore on Fiery Cross Reef. Even civilians have every right to go snorkeling there, though it might not be a good idea to try.

From a strategic standpoint, maritime possession boils down to a two-by-two matrix: if push comes to shove, can I use it, and can I stop you from using it? For Fiery Cross and its other artificial islands, the answers for China are "yes" and "yes." But for the rest of the South China Sea, China's answers are "no" and "yes" -- at least when it comes to potential conflict with the United States.

China has assiduously developed anti-access/area denial (A2/AD) capacity over the South China Sea. When the state-run Global Times threatens that China has wide selection of anti-aircraft carrier weapons, it means it. Although the US Navy might be able to counter these weapons if military exigencies required them to do so, it is unlikely that the United States would ever take the risk. There will be no American amphibious landings to open a land war in mainland China.

The problem for China is that the United States also possess A2/AD capabilities in the South China Sea, and can exercise them while keeping its prize naval assets out of China's reach. And being denied access to the South China Sea would be much more painful for China than for the United States. Even American allies like Japan and South Korea could, at modest expense, redirect trade to avoid the area in case of a conflict. The United States itself doesn't really need access to the South China Sea at all. But for China, it's crucial.

The littoral countries of the South China Sea (Vietnam, the Philippines, Malaysia, Indonesia, and Brunei) are in more of a bind. China's hand vis-à-vis them is much stronger: China can use the Sea, and it can stop them from using it. So far, all except Vietnam have hidden behind the broad American maintenance of freedom of navigation: they have behaved like free riders. It serves few American interests to allow them to do so. If the US is going to stand up for any country in the region, it should be Vietnam, if for no other reason than that Vietnam has shown real commitment to standing up for itself.

The South China Sea isn't anyone's sea. It belongs to the whole world. But the country that would suffer most from its closure in time of war would be China. Having developed A2/AD capabilities of its own, it would be hard-pressed were any country other than the United States to develop them, too. If littoral countries like the Philippines and Malaysia really want negotiating leverage vis-à-vis China, they should develop their own A2/AD capacity. If they do, China will quickly learn that while everyone else possesses workable alternatives should the South China Sea ever be closed to maritime trade, China is the one country in the region that desperately needs freedom of the seas.

Salvatore Babones is an adjunct scholar at the Centre for Independent Studies and an associate professor at the University of Sydney. This article first appeared last year.

Image: Reuters.