China, like a large majority of the world’s states but unlike the United States, has ratified the United Nations Convention on the Law of the Sea (henceforth UNCLOS). This means that China has signed up for a set of fairly specific rules about what states can claim as both territorial waters and exclusive economic zones (EEZs). Furthermore, there is an arbitration system attached to these rules. At the same time, China has for decades made some pretty ambitious territorial claims, that put it in conflict with the claims of a variety of its neighbours, including (but not limited to) Vietnam, the Philippines, and Japan. Many of these claims are simply unsupportable under UNCLOS rules. When international law comes up against Chinese maritime ambitions, norms of international dispute resolution may well suffer.

China has made these claims for decades, but has begun making them significantly more aggressively in the past couple of years, as indicated by an increasing willingness to play chicken with Japan over the Senkaku/Diaoyu islands, an increase in construction projects on features in the Spratley chain claimed by the Philippines, and the dispatch of a drilling ship with heavy naval escort into waters claimed by Vietnam. While China pursues its claims through physical force, it is likely that sooner or later, probably sooner, one or other of these disputes will get to an UNCLOS tribunal. And many of the disputes (although not the one with Japan) are based on the “nine-dash line,” a map with nine dashes showing almost the entirety of the South China Sea as part of China. This map is imprecise, the sorts of claims China is making based on it are unclear, and its historical provenance gives it no standing in international law. An UNCLOS tribunal, in other words, is not likely to find it compelling.

Maritime boundary disputes are one area where international arbitration has, over the past half-century or so, worked pretty well. Even when major powers like the United States have not received the judgments they were hoping for in disputes with weak, powerless states like Canada, they have accepted the results. States sometimes choose not to take disputes to arbitration, while cooperating over resource-sharing. This freezes the territorial dispute while allowing economic development, and eliminates the possibility of actually losing a claim. But examples of states accepting arbitration in maritime disputes, losing, and ignoring the ruling are few and far between.

China could change this in a spectacular way. States accept tribunal rulings because states accept tribunal rulings. One can read this as indicating the importance of norms, or one can read it as a functional coordination game. Either way, once a major player in global maritime politics (which China clearly is) starts ignoring rulings, what happens to everyone else’s responses and calculations?

There is, as an aside, an irony here. The United States has not ratified UNCLOS, and legally speaking is therefore not bound by its rules. But the US follows those rules anyway. China is legally bound by the rules, but seems to feel much less bound by them practically.

The upshot here is that China’s response to UCLOS arbitration, when that arbitration inevitably rules against it, will affect not just maritime claims in the South China Sea. It will threaten international cooperation in one of those areas where it has actually worked over the course of the past half-century. States have not fought over maritime boundaries for a long time. They may start doing so in the future, if accepted norms of maritime sovereignty are undermined by Chinese pursuit of its claims.