Introduction    The Sung policy of promoting stability and a status quo with neighboring states was complemented by the traditional principle of "the sage-ruler serves as a model for others, yielding peace for all under heaven." This was one of the loftiest political aims, sought by rulers in ancient China for developing mutual and peaceful coexistence with other leaders. The Sung emperors, in terms of maintaining relations and beneficial exchange with various states, upheld this ideal of peace and mutual co-existence through active official communication and commerce.    During the Northern and Southern Sung, power was focused in the central part of the land and emperors were careful not to embark on campaigns for territorial expansion. Consequently, in neighboring areas, minority groups established kingdoms and states that maintained a sometimes uneasy peace with the Sung, yet one in which cultural exchange and trade flourished. In the north were the Liao and Chin dynasties and the kingdom of Korea, while to the west and south were the regions of Turkestan, Tibet, and Ta-li, all of which developed rich cultural traditions of their own. Thus, cultural exchange and synthesis among these peoples ultimately increased the vitality, richness, and growth of Chinese culture as a whole.