It has been seen that the Emperors Kotoku and Temmu attached much importance to the development of military efficiency and that they issued orders with reference to the training of provincials, the armed equipment of the people, the storage of weapons of war, and the maintenance of men-at-arms by officials. Compulsory service, however, does not appear to have been inaugurated until the reign of the Empress Jito, when (689) her Majesty instructed the local governors that one-fourth of the able-bodied men in each province should be trained every year in warlike exercises. This was the beginning of the conscription system in Japan. THE ORDER OF SUCCESSION OF THE THRONE That the throne should be occupied by members of the Imperial family only had been a recognized principle of the Japanese polity from remotest epochs. But there had been an early departure from the rule of primogeniture, and since the time of Nintoku the eligibility of brothers also had been acknowledged in practice. To this latitude of choice many disturbances were attributable, notably the fell Jinshin struggle, and the terrors of that year were still fresh in men's minds when, during Jito's reign, the deaths of two Crown Princes in succession brought up the dangerous problem again for solution. The princes were Kusakabe and Takaichi. The former had been nominated by his father, Temmu, but was instructed to leave the reins of power in the hands of his mother, Jito, for a time. He died in the year 689, while Jito was still regent, and Takaichi, another of Temmu's sons, who had distinguished himself as commander of a division of troops in the Jinshin campaign, was made Prince Imperial. But he too died in 696, and it thus fell out that the only surviving and legitimate offspring of an Emperor who had actually reigned was Prince Kuzuno, son of Kobun.