to centralize the power of nominating and selecting appointees to office into the imperial court at Luoyang, but conflict remained between the right of evaluation between centrally-appointed Controllers and the governors of the regions. Nonetheless, the continued instability and turmoil of the Three Kingdoms period meant that the nine-rank system was not fully or solely implemented; mentions of the old nomination system as the basis for identifying talent remain prevalent in early Cao Wei writings. The nine-rank system would become more dominant in the later years of the Cao Wei regime under the regency of the Sima clan and into the early years of the Jin regime during which it had changed in nature. Under Sima Yan, the power of Controllers was expanded to include not only evaluation but also the nomination of talent, and with the conquest of Wu by Jin and the subsequent peace, the system also became more systematized and formalized. Through the changes, the ine-rank system also became more closely aligned with the interests of the powerful official clans who had come to dominate imperial politics since the Cao Wei period. The expanded powers of the appointed Controllers in turn meant that the officials who held the post, many of whom came from these clans, could use their powers to promote the interests of their own scions. While the nine-rank system helped powerful clans to dominate official posts in the court, it also helped stimulate private schooling within families as a means of transmitting knowledge that could increase one's standing as someone eligible for evaluation. An example of this intrafamilial transmission of skills is the calligrapher Wang Xizhi, of the Wang clan of Langya that was prominent during the Eastern Jin, whose sons, Wang Ningzhi, Wang Huizhi and Wang Xianzhi, were all famed calligraphers in their own right. The emphasis placed by the nine-rank system on moral attributes such as filial piety also led to the growth of "familial instructions" (), which aimed to transmit moral teachings to children, as a genre of writing in the Jin and subsequent dynasties. During the Northern Wei, ranks four to nine added additional upper and lower ranks to the standard and secondary ranks, giving the nine-rank system a total of 30 ranks (6 in the top 3 ranks; 24 from ranks 4 to 9). After the Northern Song the nine ranks reverted to the original standard of 18 ranks,