A United Nations tribunal ruled on 12.7.2016 that China’s sovereignty claims over the South China Sea, and its aggressive attempts to enforce them, violate international law. This is a necessary rebuke to Beijing, but it comes with no enforcement measures and Chinese leaders have rejected it. So its effect will depend on how China’s neighbours and the United States respond.

China by asserting “indisputable sovereignty” over an area larger than the Mediterranean and encroaching on the territory and rights of others, Beijing has threatened the rules based order that has given Asia decades of prosperity. The Hague based Permanent Court of Arbitration found that China’s main claim to the sea, represented by its notorious “nine dash line” map, has “no legal basis.” It further slammed China’s frequent claims to “historic” rights, confirming that these don’t fly under the U.N. Law of the Sea Treaty, and that there is “no evidence that China had historically exercised exclusive control over the waters or their resources.”

The ruling also undercuts China’s claims in the Spratly archipelago, off the Philippine coast, where Beijing has built and militarized seven artificial islands since 2014. It found that no feature in the Spratlys is a natural “island” under the law, so none entitles its owner to a 200n mile exclusive economic zone. That means the only exclusive zone there derives from the coast and belongs to the Philippines, confirming that China has no right to threaten Philippine commercial or military vessels as it has at places like Reed Bank and Second Thomas Shoal.

As for China’s artificial islands, the tribunal found that some are built on natural rocks that are above water at high tide and thus yield 12 mile territorial seas. But the others are built on underwater features over which no one can claim sovereignty making China an illegal occupier.

The tribunal also confirmed that China violated Philippine rights in seizing Scarborough Shoal, the 2012 incident that drove Manila to file suit. Beijing has since kept Philippine fishermen away from the 60 square mile area and may want to build an artificial island there, 120 miles from the Philippine navy base at Subic Bay.

Starting construction at Scarborough is one way Beijing may express its pique at this verdict, which Chinese spokesmen have denounced as a “farce” and “nothing more than a piece of paper.” China could also deploy additional firepower to the Spratlys and declare an air-defense identification zone over the South China Sea as it did over the East China Sea in 2013.

The better outcome would be a united front of South China Sea claimants (the Philippines, Vietnam, Indonesia, Malaysia, Brunei) negotiating jointly with China. If Beijing continues its abuses, they can file new arbitration cases, as Indonesia and Vietnam have hinted. The U.S.A is the only real enforcement authority and they have made some helpful military moves, flying A-10 attack planes from a Philippine base near Scarborough and operating two carrier battle groups in the Western Pacific. But it’s much touted freedom of navigation operations has been timid. With the Hague verdict, these operations should increase in frequency and scope. Mr. Le Drian, the French defence minister, has suggested European patrols.

A white paper issued by China's State Council Information Office also points towards a China which is set upon its present course of maintaining its hold in the SCS. The paper, titled 'China Adheres to the Position of Settling Through Negotiation the Relevant Disputes Between China and the Philippines in the South China Sea', says that the Nanhai Zhudao (the South China Sea Islands) have historically belonged to China. The paper adds that the current dispute began in the 1970s the Philippines started to invade and illegally occupy some islands and reefs of China’s Nansha Qundao (the Nansha Islands) internationally known as the Spratly Islands.

Stung by the verdict, China might very well decide to take action. Aggressive tactics by China could come in many forms setting up an Air Defence Identification Zone in the South China Sea, accelerating the reclamation of Scarborough shoal, or even an attempt to deploy military forces in waters close to its occupied and reclaimed islands.

Further, China's Defence Ministry has announced that a new guided missile destroyer was formally commissioned at a naval base in the southern island province of Hainan, which has responsibility for the SCS.

China plans to build nuclear power stations in the South China Sea to establish “effective control” of disputed islands, officials have reportedly said. The China National Nuclear Corporation (CNNC) made the announcement just two days after the Hague based tribunal concluded China had “no legal basis” for its claim to almost all of the South China Sea.

In the month leading to the G20 summit, China has sent at least 36 ships, coast guard, marine surveillance, fisheries law enforcement command into Japan’s territorial waters around the Senkaku Islands in the East China Sea. Another 200-300 fishing vessels entered the contiguous zone. Roughly 800 miles away, in the South China Sea, flotillas of Chinese barges and coast guard ships have sailed around the Philippines’ Scarborough Shoal. China and Russia are conducting a combined exercise including seizing and defending islands.  This ramped up Chinese activity has stoked fears in Tokyo and Manila that China is positioning itself to change the status quo, such as occupy the features or, at a minimum, blockade them.

Both Japan and the Philippines are taking active diplomatic measures. Japan launched a furious set of protests, requesting China to withdraw its ships from Japanese waters and prevent the reoccurrence of such situations in the future. Former President Fidel Ramos of the Philippines visited China to negotiate an agreement on maritime disputes. These diplomatic measures are appropriate and important, but diplomacy without the threat of an armed response to aggression is unlikely to succeed.

China appears to be testing opportunities on its maritime borders. U.S.A is a treaty ally of both Japan and the Philippines. The stakes for two allies are sovereign territory the highest stakes in international relations. The damage that China is doing to its reputation and the scramble of countries in the region to cooperate with the United States do not appear to deter China from engaging in provocative behaviour.

Without taking a position on the merits of all sovereignty claims, U.S.A should make it explicitly clear that it regards the Senkaku Islands and Scarborough Shoal as fundamentally different from the other territorial disputes plaguing the region. Chinese aggression against either would trigger the alliance obligations the United States has to both countries. The United States has already made this policy clear in the case of the Senkakus, but not yet for Scarborough Shoal.