Amami has a complex relationship with its southern neighbor, Okinawa. Ethnolinguistically, the languages of Amami are closer to the languages of Okinawa than to the languages of Kyushu. Politically, however, Amami shares a much longer history with mainland Japan than with Okinawa. Fragmentary sources such as a Kamakura-period map of Japan and a set of documents created by Chikama Tokiie in 1306 suggest that Amami was within the sphere of influence of the Kamakura shogunate before the Okinawa-based Ryukyu Kingdom invaded Amami in the 15th and 16th centuries. In 1609, the Satsuma Domain conquered the Ryukyu Kingdom and put Amami under its direct control. After the abolition of the Satsuma Domain in 1871, Amami was transferred to the newly established Kagoshima Prefecture, whereas the Ryukyu Kingdom was eventually replaced by Okinawa Prefecture in 1879. The Amami Islands, the Tokara Islands, and the Upper Three Islands constituted Ōshima District and were politically and economically integrated into Kagoshima Prefecture. Amami's two key industries, the (silk fabric) industry and the sugar industry, targeted the mainland Japanese market.