Wakoku (Japan) (倭国)
The term 'Wakoku' refers to a name which ancient Chinese dynasties or other countries around China used to designate a political force or its area in the Japanese Islands around that time.
It was also referred to as 'Wa.'
Wakoku was changed into 'Nihon' in official use during the latter half of the seventh century.
Summary
Several political forces of local clans (Tsukushi Province, Kibi Province, Izumo Province, Yamato sovereignty, and the Kenuuji clan) in verious areas in the Japanese Islands emerged around the middle of the Yayoi period, and these forces as a whole was referred to as Wakoku by the Chinese dynasties. It is known from the articles from "kanjo (Historical records of the Han Dynasty)" and the "Ronko (Lunheng)" that such perception of Wakoku was already present during the Former Han Dynasty. At the same time, the political forces in the Japanese Islands used the name of Wakoku to designate their country to foreign countries. The term 'Wakoku' came to be used externally.
In 57, a chieftain of Wanonanokuni (small country in Hakata area of Fukuoka Prefecture), which is believed to have been located along the Hakata Bay, had suzerain-vassal relationship with the Emperor Kobu-tei (Emperor Guangwu) of the Latter Han Dynasty, who invested him with Wakoku by giving golden stamp (Wa no na no kokuo in [the oldest known seal in Japan]), ("History of the Latter Han Dynasty"), therefore, the center of Japanese political force is believed to have been located in the northern part of Kyushu at that time.
The "History of the Later Han Dynasty" states that Suisho, the king of Wakoku, offered slaves to the Chinese Emperor in 107. For this reason, although "History of the Later Han Dynasty" was complied long afterward, one theory states that the political force representing Wakoku on some level emerged during the period from the end of the first to the beginning of the second century.
The throne of the king of Wa had been succeeded to a son since Suisho, but the the late second century saw a severe civil war among the political forces in Wakoku (=>Wakoku War). This war ended in with the accession of Queen Himiko, who lived in Yamatai-Koku (Yamatai Kingdom, 邪馬臺國・邪馬壹國; see also Yamatai-koku). Following Himiko, a male became a king of Wakoku, but another civil war occurred again, ending with accession of female Tayo (臺與・壹與, see also Tayo). In this way, during the end of the Yayoi period, a woman was sometimes allowed to ascend the throne.
After the rule of Tayo, there were no records that the Wakoku ruler had offered tribute to the Chinese dynasties for a few centuries, but around the late fourth century, records of tribute to the Southern Dynasty, including the Eastern Jin dynasty, were found and the tribute had been sent intermittently till the end of the fifth century.
There were references to the kings of Wakoku during that time in the history books of China, who were called the five kings of Wa, such as San, Chin, Sei, Ko, and Bu,
According to one belief, the five Kings of Wa, who intended to intervene in Gaya, located in the southern part of Korea, for acquiring concessions of natural resources there from the latter half of the fourth century, dispatched an envoy to China to submit to a suzerain-vassal relationship with the Chinese sovereign so that they might make use of such a relationship on the pretext of their intervention in Korea.
While the King of Wa called himself the King of Wakoku, or the King of Wa to the dynasties in the Asian Continents, in the country, he called himself the king or the great king (Yamato sovereignty), or amenoshitashiroshimesu okimi (the title of the king of Wa), judging from an iron sword carved with letters, ' 台天下獲□□□鹵大王 (the title of king),' which was excavated in the Eta Funayama Tumulus in Kumamoto Prefecture. One theory becomes popular that around that time, Wakoku began to be conscious that it was another realm of China.
The "Suishu (the Book of the Sui Dynasty)" states that Tarishihiko, the King of Wakoku, signed his name as the Emperor of the land where the sun rises, not the King of Wakoku, on the sovereign's message carried by a Japanese envoy to Sui Dynasty China dispatched by him in 607. The "Daichidoron (Commentary on the Great Wisdom Sutra, "摩訶般若波羅蜜多経," literally translated to the "Heart of the Perfection of Transcedent Wisdom")" written at that time indicated that such expression as the land where the sun rises only referred to the East of China, but some people mention that the expression of the King of Wa was avoided. From then on till the latter half of the seventh century, the name designating the country was still Wakoku or Wa, but in the process of remodeling its state and administrative apparatus on the ritsuryo system (a system of centralized government based on the ritsuryo code) by the Emperor Tenmu, there was growing national awareness about the avoidance of using Wa or Wakoku, so that before and after 701, a pair of Chinese characters, 日本, (meaning of 'the land from the sun-rise) came to be used. At first, the characters were read in the Japanese way as 'Yamato,' and then read 'Jippon,' or 'Nippon,' which became established during around the Heian period, led up to the present day.
In the Medieval Muslim world, "The Book of Routes and Kingdoms" written by Ibn Khurdadhbin during the ninth century and the "Thousand and One Nights (Arabian Nights)" described the place name of 'waqwaq,' located to the east of China and India, which is believed to have been 'Wakoku (Wa-qwaq)' designating Japan.
Different opinions
According to the theory of the Kyushu dynasty, Wakoku had been founded by the first century around the area of the northern part of Kyusu, and the King of Wa placed the capital in Wanonanokuni near the Hakata Bay and offered tribute to the Han Dynasty, and then transferred it to Dazaifu (govermental headquarters in northern Kyushu from the late Kofun period (300-700) through the Heian Period) to exist till the end of the seventh century. However, there is no peer-reviewed paper on the subject of the Kyushu dynasty, neither was there a historian, nor an archaeologist who accepts this theory.