status, for example, by granting each other the highest positions as the most esteemed envoys. As the Wei Shu and Song Shu testify, there was a shift from imperial rhetoric denouncing the other side as illegitimate barbarians, towards a new conception referring to the two as distinct 'Northern' and Southern' parallels, using unique local customs to distinguish themselves and compete for legitimacy. Under the later waning leadership of the Chen dynasty, the southern Chinese were unable to resist the military power amassed in the north by Yang Jian, who declared himself Emperor Wen of Sui and invaded the south. The Southern dynasties, except for the last Chen dynasty, were strongly dominated by the shijia, the great families, who monopolised political power until the mid-6th century. This class was created by Cao Cao during the late Han dynasty when he attempted to consolidate his power by building an endogamous military caste of professional soldiers. This led to the rise and usurpation of the Sima family who ruled the Jin dynasty, and subsequent leaders were similarly unable to bring the other great families in line. When the Jin dynasty fled south, the weakness of the central government was greatly exacerbated, and the great families who accompanied the Emperor in his flight, along with the most wealthy clans of earlier settlers along the Zhejiang coast, were the primary power of the Eastern Jin. With the greatly increased importance of proving one's pedigree to receive privileges, there was a rise in compiling of genealogy records, and the great families moved to legally outlaw intermarriage with common families. The lower class Northern migrants were forced to become "guests" (dependents) of the great families who established private guard forces. When the Eastern Jin attempted to draft the dependents of the great families, they were quickly overthrown. However, with the fall of the Eastern Jin in 420, the balance of power shifted in favour the central government. The subsequent Liu Song, Qi, Liang and Chen dynasties were ruled by military leaders from low social status backgrounds. They gradually stripped the powerful clans of military power, authority and wealth. They stationed regional armies around the country under the command of the imperial relatives, and recruited officers from humble backgrounds. They appointed low-level officials to monitor the powerful elites in the top government posts. The southern aristocracy declined with the rise of the Indian Ocean trade in the mid