The Ryukyus remained nominally independent, an "exotic realm" (異国, "ikoku") to the Japanese. The kingdom's royal governmental structures also remained intact, along with its royal lineage. However, Amami Ōshima and a number of other northern islands now known as the Satsunan Islands were annexed into Satsuma Domain, and they remain today within Kagoshima Prefecture. Though the king retained considerable powers, he was only permitted to operate within a framework of strict guidelines set down by Satsuma, and was required to pay considerable amounts in tribute to Satsuma on a regular basis. Efforts were also made to obscure Satsuma's domination of Ryukyu from the Chinese Court, in order to ensure the continuation of trade and diplomacy, since China refused to conduct formal relations or trade with Japan at the time.