The Ryukyu Kingdom was a kingdom in the Ryukyu Islands from 1429 to 1879. It was ruled as a tributary state of imperial Ming China by the Ryukyuan monarchy, who unified Okinawa Island to end the Sanzan period, and extended the kingdom to the Amami Islands and Sakishima Islands. The Ryukyu Kingdom played a central role in the maritime trade networks of medieval East Asia and Southeast Asia despite its small size. The Ryukyu Kingdom became a vassal state of the Satsuma Domain of Japan after the invasion of Ryukyu in 1609 but retained de jure independence until it was transformed into the Ryukyu Domain by the Empire of Japan in 1872. The Ryukyu Kingdom was formally annexed and dissolved by Japan in 1879 to form Okinawa Prefecture, and the Ryukyuan monarchy was integrated into the new Japanese