In the meantime, feudalism established itself in the country. Side by side with the effeminate aristocracy of the _kuges_, certain nobles descended from collateral branches of the Imperial family, and who in their time had occupied great official positions, both in the provinces and in the capital, leaving subalterns to fulfil their duties, now formed themselves into a military and territorial aristocracy, and, whilst profound peace reigned in the greater part of the country, carried on a war against the Koreans in its south-eastern limits, and against the Ainos, who had been driven back to the north of Hondo, in the north-east. The custom imported from China by the Japanese of separating the civil from the military functionaries, combined with a genius for heredity, led in the course of time to the creation of many great military families, under whose authority or lead clans of soldiers grouped and gradually separated themselves from the rest of the population. The chiefs of these clans in due time became, especially in the tenth century, in the north and eastern provinces, independent, so that by degrees their influence during the two succeeding centuries in the Government was paramount, and the Court of Kioto was the object of perpetual dissensions between two great military families, the Taira, and the Minamoto, both descendants of Emperors of the eighth and ninth centuries. They had each a claimant to the Imperial throne, who was invariably an infant. A Taira, Kiyomori, governed Japan from 1156 to 1181 in the position of Prime Minister. He ordered the Minamoto family to be massacred; one or two of its members, however, escaped, among them Yoritomo, the son of the chief. In due course of time this Yoritomo created a revolution in Kwanto in his own favour. Upon learning of the death of Kiyomori he straightway marched upon Kioto in company with his bastard brother, Yoshitsune, who had escaped from a monastery to which he had been relegated. Between them they seized the capital and proclaimed a child of seven years of age Emperor in the place of the Mikado Antoku, who was not much older, and who was carried off by the Taira to the island of Kiu-Siu. The great naval battle of Dan-no-ura, won by Yoshitsune in 1185 at the mouth of the Inland Sea, completed the ruin of the Taira, who, together with their Emperor, were nearly all slain in the disaster to their fleet, which made Yoritomo master of Japan.