Increasingly used to elbowing its maritime neighbours aside with the swagger of a local bully, China is unhappy about the prospect of being told what to do by an obscure court in the Netherlands.

The Permanent Court of Arbitration, set up in The Hague over a century ago to handle disputes between member countries, will issue a decision on Tuesday on a complaint brought three years ago by the Philippines about China's behaviour in the South China Sea.

It's widely expected the ruling will come down on the Philippines' side. Even China seems to think so.

Calling the tribunal a "law-abusing farce" with no jurisdiction, and the impending ruling a "piece of trash paper," China has boycotted the entire proceedings.

Instead, it is blocking off a big chunk of the disputed sea area for a major military exercise, taking out full-page ads in the world's newspapers and mounting a diplomatic full-court press to make the case it has refused to make before the tribunal.

An FA-18 jet fighter lands on the USS John C. Stennis aircraft carrier in the South China Sea on April 15, while U.S. Defence Secretary Ash Carter visited the aircraft carrier. (Associated Press) Long-standing disputes among the countries that share the South China and East China seas with the Peoples' Republic have become more bitter and dangerous with China's growing military and financial muscle.

Basing its claims mostly on an old map of uncertain provenance that it has lodged with the United Nations, China asserts sovereignty over everything inside a "nine-dash line" encircling about 90 per cent of the sea around its coast, engulfing the rival overlapping claims of Japan, Taiwan, Vietnam, the Philippines, Malaysia and Brunei.

There's a lot more at stake here than national pride. One-third of the world's shipping, commerce worth about $5-trillion a year, navigates these waters, and there are large oil and gas deposits beneath the surface.

Creating islands

For two years China has been engaged in huge land reclamation projects, dredging up vast quantities of sand to transform reefs, islets and rocks that used to be submerged at high tide into islands with a total area of more than 1,000 hectares.

During his visit to Washington last year, President Xi Jinping, promised "not to militarize" these artificial islands, but satellite images reveal extensive airstrips and military installations.

Out-manoeuvred on the high seas, the Philippines took to the courts in 2013 with a carefully crafted challenge to China under the United Nations Convention on the Law of the Sea.

A military plane carrying international journalists on March 23 provides an aerial view of the Taiwan-controlled Taiping island, also known as Itu Aba, in the South China Sea. (Associated Press) China not only helped negotiate the UN convention, it was one of the first countries to sign it in 1982 and ratify it in 1996.

The Law of the Sea gives countries 12 nautical miles from shore as territorial waters, and 200 nautical miles as an exclusive economic zone. It also clearly states that sovereignty claims cannot be based on features that are under water at high tide, or on man-made islands.

The Philippines case neatly sidesteps the tangle of rival claims to sovereignty, saying simply that no matter who owns the disputed reefs and islets, they can't be used to justify large claims over the surrounding waters.

Most damaging to China, the Philippines also argues that the Law of the Sea, with its clearly agreed limits, rules out the vast "nine-dash line" claim.

One of the reasons China has refused to take part in the arbitration is that its own case seems extremely weak.

"China was the earliest to explore, name, develop and administer various South China Sea islands," Foreign Minister Wang Yi said earlier this year. "Our ancestors worked diligently here for generations."

'Because I say so!'

An argument based vaguely on antiquity and a line someone once drew on a mysterious old map has about the same force in international law as the legal precedent so frequently invoked by moms the world over: "Because I say so!"

After Mao Zedong died 40 years ago, China began working patiently to undo decades of poverty and isolation to return to what it considers its rightful place on the world stage.

Chinese dredging vessels are purportedly seen in the waters around the disputed Spratly Islands in the South China Sea. This image is from video taken by a Poseidon surveillance aircraft on May 21, 2015. (U.S. Navy/Reuters) The Law of the Sea convention was a milestone in that journey, along with resuming diplomatic relations with former enemies, taking China's seat at the United Nations, and joining the World Trade Organization.

After careful decades of joining the complex architecture of international relations, China is beginning to assert a superpower's right to ignore it.

Asked about the upcoming ruling, which is binding on China even though it has not taken part, Foreign Ministry spokesman Lu Kang said, "We will not accept it or recognize it."

All the countries involved, including China and the United States, which has treaty obligations to defend many of China's neighbours, have a clear interest in keeping the lid on a potentially disastrous conflict.

Counting on others to back down

President Xi Jinping, who took office just under four years ago, is dramatically changing China's approach, calculating that others will back down rather than confronting China as it gradually grabs what it wants.

So far, his calculation that the United States under President Barack Obama will let things slide appears to be correct. But there's a changing of the guard coming in Washington.

The most likely winner of November's U.S. presidential election will certainly be inclined to demonstrate how forceful and decisive she can be, while the other candidate is almost as fond of bluster and bullying as China is.

Where it used to preach negotiation, dialogue and the five basic principles of peaceful coexistence, China seems bent on stirring up angry, insulted neighbours and poking the next president of the United States with a stick.