Maritime trade in East Asia began to flourish in the seventh and eighth centuries C.E. It was jump-started by Persian and Arab merchants, who traveled to and settled in ports as far from home as Guangzhou (Canton) in southern China. Later, commerce spread eastward and northward along the coast to Quanzhou, Fuzhou, Mingzhou (Ningbo), and finally Hangzhou, where merchants could gain access to the Chinese interior via the Grand Canal. Foreign trade thus became integrated to a certain extent with China's domestic economy. Although pioneered by Arabs and Persians, this route soon fell under the domination of ethnic Chinese. Meanwhile, Korean merchants established their own trade networks connecting the west coast of Silla with Laizhou, Haizhou, and other ports in north China and entering the canal system through the mouth of the Huai River. In the early ninth century, semiautonomous communities of Korean traders were scattered along much of the north China littoral.SOURCE: Gateway to Japan: Hakata in War and Peace, 500–1300, by Bruce L. Batten (U. Hawai‘i Press, 2006), pp. 111-112
These northern routes were further extended to Japan under the direction of the Korean tycoon Chang Pogo. Chang himself is said to have visited Kyushu in 824 and met with the governor of Chikuzen, although the validity of this account has been questioned. In any case Chang, acting by authorization of the king of Silla, was in charge of maritime defenses at the Ch'ŏnghae garrison on Wan Island by the late 820s or early 830s. It is probably no coincidence that the first Japanese record of "Silla merchants" in Hakata dates from 831.
However, Korean domination of the Hakata trade was short-lived, to say the least. Merchants from Tang make their first known appearance in Hakata in 842, and soon thereafter they completely replace their counterparts from Silla. Chinese merchants bypassed the Korean coastal route entirely, traveling directly across the East China Sea from locations such as Fuzhou and Mingzhou. These same ports continued to supply the bulk of foreign merchants visiting Japan after the demise of Tang (in 907), when they fell under the control, respectively, of the Wu Yue kingdom and then (after 978) the Song empire.