Following the Satsuma conquest of the Ryukyus in the first decade of the 17th century, Okinawans were required to pay a tribute of 90,000 koku (defined as the quantity of rice sufficient to feed one person for one year. That came to approx 330 pounds). That didn't leave much rice left over for the Ryukyuans to sustain themselves. The introduction of sugar and sweet potatoes, the two major crops and their exploitation for home consumption and for the export trade marked an abrupt shift in the basic economy of the Ryukyu Islands from dependency on wide-ranging free commerce to a niggardly share in the China trade and the production of two crops with which to sustain life within the islands.|
The gentry at Shuri lost much of their independence of action, but the peasants in the hinterland became more important to the government and were stimulated to greater production. [Source: Okinawa: The History of an Island People, Kerr, 1958; and Wikipedia].