In 645, Prince Naka-no-Oe together with Fujiwara no Kamatari led a coup to oust the powerful Soga clan of their control over the Yamato court. Then Kamatari and Prince Naka-no-Oe who became Emperor Tenji’, put in place a series of codifications of law based on the Chinese model of central government. Collectively, the codes are known as the Taika Reforms and they had the effect of reforming the political system into a centralized government by the emperor.
Some of the most important arrangements written into the penal and administrative codes were:
The restructuring of ranks in the administration of central affairs: the Asuka no Kiyomhara code of 689 added the office of 3 ministers the chancellor (daijo daijin), the minister of the left and the minister of the right, to the Council of State. Later, more offices were added to shape the imperial government along Chinese lines. The government was run by a system of offices ranging from those closest to the emperor to others at more at lower levels and from remote places.
Under the emperor, were the two most important councils, the Council of State which ran the secular affairs of state, and the Council of Kami Affairs that oversaw all matters involving kami worship. The highest official was the Council of State’s chancellor who was served by the minister of the left and the minister of the right. Below these top ranking officials were four senior counselors. In consultation with one another, counselors and ministers made important policy decisions and recommended appointments and promotions for high-ranking officials. Each of the ministers of the left and right were responsible for four ministries that handled a range of court affairs, and matters relating to personnel, treasury, budget, household registers, taxes, irrigation, paddy fields. Inside each ministry were administrative organs of three types: secretariats (shiki); bureaus (ryo) and offices (tsukasa).
The reforms served to put the emperor at the apex of the state, strengthening the sacred and secular authority of the ruling emperor. The codes placed no limitations on imperial authority, thus allowing the emperor despotic control.
One important reform had to do with the surveying and registering of lands and population. The reform created a system for keeping track of households instituted in 670 with the appearance of household registers (koseki) – which was important because for assessing taxes from the land and services from the people.
Another important reform involved the nationalization of land. Paddies were henceforth allocated centrally by the government: every 6 years, all free adult males received 0.3 acres, females 0.2 acres.
The tribute collection system was also revised. Tribute used to be collected based on the area of land cultivated by a household until 680, but thereafter tribute was collected from individuals.
The implementation of the district system. Before 673, local affairs were administered by the clan chieftains but after that date, the local sixty provinces were divided into districts (kori) containing villages (sato) of 50 households each, all coming under the jurisdiction of the imperial court.
Another reform involved required taxation in the form of produce, in addition to corvee labour.
Conscript duty was imposed and each household had to send one young male conscript.
Unauthorized weapons were confiscated from all over outlying provinces to prevent insurgencies.
The establishment of a strong centralized government had the side-effects of diminishing the prominence of clan families that were local strongholds of power. Families that controlled the imperial family changed and waxed and waned with the times. Since the 4th and 5th century until the Taika Reform, each region of Japan was under the control of the powerful and near-autonomous wealthy family Gozoku. The consequence of the Taika Reform and the establishment a strong central government by the Japanese Royal Family was therefore the exclusion of the Gozoku power and authority.