The fall of the house of the Soga may be ascribed to several causes. In the first place, it became an absolute necessity for the growth of the imperial power to get rid of the too arrogant Soga ministers, because to bear with them any longer would have endangered the imperial prestige itself. Secondly, as soon as the family of the Soga had ceased to fear its rivals, it began to be divided within itself by internal strife. Lastly, a quarrel about the imperial succession brought about the interweaving of the above two causes. The Prince Naka-no-Oye, being the eldest son of the Emperor Jomei, was naturally one of the candidates to the throne. As his mother, however, was the Empress Kokyoku, and therefore not of the Soga blood, the Prince was in fear lest he should be put aside from the order of the succession. Besides, he was very much enraged at the overbearing attitude of Yemishi and his son. The Nakatomi family to which Kamatari belonged was one of the five old illustrious names, and had been chiefly engaged in religious affairs. Kamatari deeply deplored the fact that his family had long been overshadowed by that of the Soga. Being qualified as a capable statesman, he foresaw the political danger to which Japan was exposed at that time. The lateral branches of the Soga family, actuated perhaps by jealousy against the main branch, joined the Prince and Kamatari in annihilating the far too overgrown power which threatened the imperial prerogative. Japan thus safely passed this political crisis. The next task was the thorough reconstruction of the social and political organisations, and the establishment of a uniform system throughout the whole Empire. A series of grand reforms was inaugurated in the year 645 A.D. in the name of the reigning Emperor Kotoku, who was one of the uncles of the Prince on his mother's side, and ascended the throne as the result of wise self-denial on the part of the Prince. The first reform was the initiation of the period name, a custom which, in China, had been in vogue since the Han dynasty. The period name which was adopted at first in Japan in the reign of the Emperor was Tai-Kwa. This Chinese usage, after it was once introduced into our country, has been continued until today, though with a few short interruptions.