|A Japanese painting of a Chinese junk then plying the Japan trade|
Under Koxinga, for any merchant ship trading in Japan, each must pay an annual licensing fee which ranged from 500 to 2,100 taels of silver, varying by the tonnage of the ships. Koxinga's Japanese brother 田川七左衛門 was charged with collecting the fees and enforcing licensing renewal, the latter in collaboration with officials in Nakasaki where the Chengs had enjoyed cordial relations with the ruling Daimyo. To trade with Taiwan, before the Dutch were driven away by Koxinga, 何斌* was put in charge of licensing.
[*He Bing何斌 had worked for Dutch East India Co as its linguist representing the Company interest in dealing with the Aborigines. He ran afoul of the Company rule for conducting some illicit activities. Before his arrest by Frederic Coyett, he had fled back to Hokkien, in time to report to Koxinga the riches of Taiwan. With info on the Dutch defense, especially the passage bypassing the defense of Ft Zeelandia, Koxinga decided to re-take his father's land.]
All along, the Japan trade was of the utmost importance to the Cheng Clan. The licensing fees were simply a source of additional revenues, the Cheng Clan had also funded their own shipping operation while leasing cargo space to other traders at the same time. The Japan trade became even more important by the time 鄭經Cheng Ching assumed the leadership of Tung Ning Kingdom. This was when Taiwan became the gateway of European trades to Japan.
The Qing closure of coastal areas of southern China to Ming-Cheng had intended to choke off the supply of Chinese merchandise. While the retaking of Amoy in 1666 had relieved the pressure somewhat, in times of war, however, shipping traffic often slowed to a crawl.
It should be noted that merchants who traded with Ming-Cheng were not ordinary businessmen. They remained loyal to the Ming Court even though they were now ruled by the Qing. Those who could afford the bribes paid to border patrols gained ready access to Amoy directly. Those who could not, often carried raw silk on their backs, traveled by back roads, got on tiny fishing sampans, risking everything to reach Amoy. Likewise, to facilitate smuggling of foreign goods into China, bribing of officials, especially low-level border guards become the secret weapon of the Cheng Clan and their associates.
Smuggling and bribery, going hand in glove, had continued after the fall of Ming-Cheng except it was not for just merchandises, people, as well. Throughout the early Qing rule, people migrated from the Mainland to Taiwan by sea, to seek a better life. And 212 years of revolts, "三年一大反五年一小反"，against the Qing carried on until 1895, when the island, together with its people, was abandoned and ceded to Japan by the Chinese.