In the pre-war period, when the ultra-nationalism prevailed, Tsuda Sokichi cast serious doubts on the official theory that the emperor was in a direct line of descent from the "Great Sun Goddess" Amaterasu. In line with this assertion, he suggested that the hereditary line of succession of the emperorship by the Imperial Family was finalised by the death of the Emperor Buretsu in 506 A.D. Following the rebirth of free intellectual inquiry after the Pacific War, the Tsuda theory was expanded in various ways. For example, Mizuno Yu presented "Changes of Dynasties Theory" (Ocho Kotai Setsu), claiming that the ancestor of today's Imperial Family acceded to the throne not in 660 B.C., as the Nihonshoki says, but in 500 A.D. for the first time and that there were two preceding dynasties. The other attempt in the pre-war period, Kida Sadakihi's "Double Dynasty Theory" (Ryocho Heiritsu Ron) claimed that two dynasties co-existed side by side from 534 to 539. This showed sharp contrast to the officially authorized theory of "single line" rule (bansei ikkei) by Japan's Imperial House. After the war, Hayashiya Tatsusaburo, a successor of Kida theory defined the early 6th century as the "period of civil war". Hayashiya claimed that the civil war started in 527 when Iwai, a local ruler of the Tsukushi Province, caused a rebellion (this rebellion itself was suppressed in the same year) and that it lasted for thirteen years until the death of Senka in 539. This theory has received popular support. Although having been widely supported the "Changes of Dynasties Theory" is open to question from a variety of reasons. Firstly, the enthronement of the Emperor Keitai in 507 A.D. has been regarded as a beginning of a new dynasty because he did not belong to the Imperial family member in the capital but lived in the country and claimed to have been "a descendant in the fifth generation of the Emperor Ojin" which appears to be doubtful. However, a careful reconstruction of the Imperial family tree reveals that all the princes and their descendants of the Emperor Nintoku, the son of Ojin, had been dead, either killed by their political enemies or died a natural death, by the year 507. Therefore the descendants of Ojin became eligible as a successor of emperorship in 507. Accordingly, even such a remote descendant as Keitai had a good enough chance to be selected if he obtained strong support from ruling aristocrats. Secondly, the same politicians who actually ruled the country such as Otomo-no-Kanamura and Mononobe-no-Arakahi kept the office continuously before and after 507, which means there was no drastic change in the political body at that time. The reexamination of the Kida-Hayashiya theory proved that it rests on shaky ground ; in fact there are few positive reasons to support it. The writer presents a theory that Keitai died in around 518 or 519, not in 531 as the Nihonshoki states, and was succeeded by Ankan who reigned for several years. Ankan was succeeded by Senka who was assassinated by his political rival Kinmei. Kinmei acceeded to the throne in 531. The coup d'etat was carried out by the Kinmei group as they thought Kinmei was the "main stream" successor of the emperorship since his mother was a daughter of a previous emperor, whereas the mother of Ankan and Senka was of low birth. The most important economic policy which was originated by Keitai and followed by his successor Ankan was to establish new miyake or imperial storehouse compounds with large scale ricefields around them and to reorganise old miyake. This was in order to prepare for the military expedition to south Korea where Kara, a group of small kingdoms which were within a Japanese alliance, was in jeopardy.
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