У Цзэтянь
In the early period of the Tang dynasty, because all the emperors were her direct descendants, the evaluation for Wu Zetian were relatively positive. Commentary in subsequent periods, however, especially the book "Zizhi Tongjian" compiled by Sima Guang, criticized Wu Zetian harshly. By the period of Southern Song dynasty, when Neo-Confucianism was firmly established as the mainstream political ideology of China, their ideology determined the evaluation for Wu Zetian.