Since China first began trading with the world more than 2,000 years ago, it has opened and closed like a clamshell. During the Tang dynasty the clamshell was wide open and remained so for many centuries. A string of inventions—gun­powder, paper, printing, and cast iron—had set China on course to become the world's leading economic power. Trade with the West had steadily expanded, with Chinese seafarers taking an increasingly dominant role.

When the great admiral Zheng He set sail in 1405 with a fleet of 317 ships, China ruled the waves. "If you had been sitting in a spaceship looking down on Earth, and you had observed developments from the ninth to the 15th century," says John Miksic, "you would have thought that the Chinese would take the next step—explore the Atlantic and become the dominant world culture." But throughout Chinese history, there has been another, equally powerful force at work: a distrust of merchants and the foreign influences they import, dating back to Confucius, who believed trade and commerce should not dictate Chinese culture and values.

In A.D. 878, little more than half a century after the Belitung ship sank, a rebel leader named Huang Chao burned and pillaged Guangzhou, killing tens of thousands of Muslims, Jews, Christians, and Parsis. And not long after Zheng He's voyages, when Columbus reached the New World, the Confucian worldview won the day; China burned its fleet and turned inward. The Silk Road and the Maritime Silk Route, which had linked China to the world, lapsed into disuse. The Portuguese entered the Indian Ocean, and by the late 17th and early 18th centuries, Europe had begun to dominate world trade. "The whole of world history would have been different if the Chinese had not gone into their shell for 500 years," Miksic says.

Now China competes with India to be the world's workshop. China is open as never before and once again trading with its ancient partners in the Middle East. Iran, for instance, supplies 12 percent of China's oil. In return, Beijing provides machinery and locomotives, builds subways and railroads, and helps Tehran exploit its vast mineral resources, closing the loop from the ninth century, when cobalt was shipped from Persia to China for the blue-and-white ceramics found on the Belitung ship.

"The ancient networks are restored through industries and factories in a world that is now globalized," says Wang Gungwu, a historian at the National University of Singapore.

For how long this time is anybody's guess.