1,300 years of Chinese history. Leaders of the southern states that claimed the title of emperor were instead referred to as "ruler" (主). The final chapters of the Zizhi Tongjian deal with the Southern Tang. They provide significant amount of information about the state. Sima Guang opined that conquering the north was beyond the capabilities of the Southern Tang. Contemporary scholars have noted that the personal biases of Sima Guang at times removed a sense of objectivity in the text. The ideological stances of the Zizhi Tongjian greatly influenced subsequent Song historiography, and are still prominent in modern scholarship. The Wudai shiji largely followed the Zizhi Tongjian in its treatment of the Southern Tang. However, the work has been seen as less accurate by contemporary scholars. In the work Ouyang defined the histographical concept of the Ten Kingdoms (十國). He also wrote a treatise on political legitimacy, determining that the principal factor lay in controlling a unified Chinese state. He laid out how to determine the legitimacy of a regime without necessarily giving into personal or cultural biases. He postulated that there were interregnums where no authority was necessarily legitimate. In 1355 Yang Weizhen wrote an essay critiquing the recently published Song shi. In it he questioned the prevailing belief that the Southern Tang were not a legitimate political entity. He recorded statements from Taizu and Qubilai that supposedly demonstrated the importance of controlling Southern China to acquire political legitimacy. Neither quotation appears in any other historical sources, making them of doubtful authenticity. "Five Demons" The Song political experiences influenced the depiction of the Southern Tang in their historical works. During the reign of Emperor Zhenzhong a group of financial and political reformists were derided as the "Five Demons" by opposing interest groups. This designation was later employed by Song historians to describe xiaoren 小人 officials that made a faction to illicitly gain power in the Southern Tang government. Membership in this ostensible group varies somewhat between the sources. It was however almost always affiliated with Song Qiqiu in some capacity. The existence of this supposed faction has been critiqued by Johannes Kurz as a product of the personal biases of Song historians and their deliberate rearrangement of historical materials. The Diaoji litan was the first work to employ the term. The claimed members of this group were Song Qiqiu, Chen Jue, Feng Yanji, Feng Yanlu, and Zha Wenhui 查文徽.