The Ryukyu Kingdom (Ryukyuan: 琉球國 (ruchu－kuku), Japanese: 琉球王國ryukyu-o-koku), Traditional Chinese: 琉球國 (liuqiuguo)) was an independent kingdom which ruled most of the Ryukyu Islands from the 15th century to the 19th century. The Kings of Ryukyu unified Okinawa Island and extended the kingdom to the Amami Islands in modern-day Kagoshima Prefecture, and the Yaeyama Islands near Taiwan.

In the three Ryukyu historical annals—Chuzan Seikan (中山世鑑, Mirror of Chuzan), Chuzan Seifu (中山世譜, Genealogy of Chuzan), and Kyuyo (球陽, Chronicle of Ryukyu)—the history of the Ryukyu Kingdom began with the Tenson Dynasty (天孫王朝, Dynasty of Heavenly Descent), which was said to have lasted 17,000 years. Many historians today believe that this is a mythological legend created in the 16th or 17th century to lend more legitimacy to the ruling dynasty, the Sho family, over other local aristocratic families.

The Tenson Dynasty ended with three kings of the Shunten Line (舜天王朝), lasting from 1187 to 1259. According to Chuzan Seikan, written by Sho Shoken, the founder of the dynasty was a son of Minamoto no Tametomo, a Japanese aristocrat and relative of the Imperial family. Minamoto no Tametomo was exiled to the Izu Islands after he failed to gain power in the Kyoto court; he then fled and drifted to Ryukyu, where his son Shunten established their own dynasty. Some Japanese and Chinese scholars claim that the Shunten dynasty was again invented by the Sho family historians, for the same reason that they created the Tenson legend.

In the 14th century, small domains scattered on Okinawa Island were unified into three principalities: Hokuzan (北山, Northern Mountain), Chuzan (中山, Central Mountain) and Nanzan (南山, Southern Mountain). This was known as the Three Kingdoms or Sanzan (三山, Three Mountains) period. These three principalities, or tribal federations led by major chieftains, battled, and Chuzan emerged victorious, receiving Chinese investiture in the early 15th century. That is to say, the leaders of Chuzan were officially recognized by China as the rightful kings over those of Nanzan and Hokuzan, thus lending great legitimacy to their claims, if not victory outright. The ruler of Chuzan passed his throne to king Hashi; he received the surname "Sho" from the Ming emperor in 1421, becoming known as Sho Hashi, 尚巴志). Hashi had already conquered Hokuzan in 1416 and Nanzan in 1429, uniting the island of Okinawa for the first time, and founding the first Sho Dynasty.

Sho Hashi adopted the Chinese hierarchical court system, built Shuri Castle and the town as his capital, and constructed Naha harbor. Several generations later, in 1469, King Sho Toku died without a male heir; a palatine servant declared he was Toku's adopted son and gained Chinese investiture. This pretender, Sho En, began the Second Sho Dynasty. Ryukyu's golden age occurred during the reign of Sho Shin, the second king of that dynasty, who reigned from 1478-1526.

Major events
•1372 The first Ming dynasty envoy visits Okinawa, which had been divided into three kingdoms, during the Sanzan period. Formal tributary relations with the Chinese Empire begin.
•1419 Chuzan, led by Sho Hashi, occupies Nakijin gusuku, capital of Hokuzan.
•1429 Chuzan occupies Shimajiri Osato gusuku, capital of Nanzan, unifying Okinawa Island. Sho Hashi establishes the Kingdom of Ryukyu, ruling as king with his capital at Shuri (now part of modern-day Naha).
•1470 Sho En (Kanemaru) establishes the Second Sho Dynasty.
•1477 The third king, Sho Shin, ascends to the throne. Golden age of the kingdom.
•1609 (April 5) daimyo (Lord) of Satsuma in southern Kyushu conquers the kingdom. King of Ryukyu becomes a Japanese vassal.
•1624 Lord of Satsuma annexes the Amami Islands.
•1846 Dr. Bernard Jean Bettleheim (d. 1870), a British Protestant missionary, arrives in Ryukyu Kingdom. He establishes the first foreign hospital on the island at the Nami-no-ue Temple.
•1853 Commodore Matthew Perry of the US Navy visits the kingdom. Bettleheim leaves with Perry.
•1866 The last official mission from the Qing Empire visits the kingdom.
•1874 The last tributary envoy to China is dispatched from Naha.
•1879 Japan replaces the Ryukyu han with Okinawa Prefecture, formally annexing the islands. King Sho Tai (尚泰) is given the title of marquis (藩王 Han'o) and removed to Tokyo.

Reference

http://en.wikipedia.org/wiki/Ry%C5%ABky%C5%AB_Kingdom