Okinawa, previously controlled by a number of local chieftains or lords, loosely bound by a paramount chieftain or king of the entire island, split into these three more solidly defined kingdoms within a few years after 1314; the Sanzan period thus began, and would end roughly one hundred years later, when Chūzan's King Shō Hashi[1] conquered Hokuzan in 1419 and Nanzan in 1429.

Seii's reign was relatively short, and defined by the interference and political abuses of his mother which led to an erosion of what little support the young king may have had from the territorial lords.

It is important to note that the three "kingdoms" were little different from the loosely unified chiefdoms which came before, and the "kings" did not wield considerably greater power, nor were their administrations more organized or more politically stable than what came before.

Seii was overthrown by the lord of Urasoe around 1349–1355; the reign of the new king, Satto, marked the emergence of Chūzan as a small but not insignificant player in regional trade and politics.

From then on, Chūzan (and unified Ryukyu later) would send frequent tribute missions, and would rely upon the Chinese court to officially recognize each successive Ryukyuan king with a formal statement of investiture.

China would have an incredibly strong influence on Ryukyu for the next five hundred years, politically, economically, and culturally, as it did with its numerous other tributary states.

Though China accepted tributary missions from Hokuzan and Nanzan as well at this time, they officially recognized only the King of Chūzan as a head of state in Ryukyu.

In the intervening years, he formally succeeded his father to the throne and received investiture and the dynastic family name "Shang" (尚, Shō in Japanese or Okinawan) from the Ming court.