The origin of the Jingpo remains open to debate. Chinese ethnohistorians generally hold that the ancestors of the Jingpo originated in the Tibetan Plateau, around the sources of the Irrawaddy, Nu (Salween), Lancang (Mekong), and Changjiang (Yangzi) rivers, and moved south about 1,500 years ago. Their southern migration diverged along eastern and western routes: the western route went along the N'mai Hka and Nu rivers into the triangle between the N'mai Hka and Mali Hka rivers and its western areas; the eastern route went along the Jinsha (upper reach of the Yangzi) and Yalong rivers into the old Langsudi and its eastern area. From the thirteenth century on, the eastern route migrants turned west into the area of Pianma, Togo. Some of them then moved northwest to Hkamti Long and to Assam, some went westward to the Huhkawng Valley and southward to the jade mines near the Burma border, and some migrated southward along the Irrawaddy into the area north of the Shan State of Burma. Among those southbound migrants were the Jingpo, who entered Dehong in about the fifteenth century. The reasons for the southward movement were the harsh environment, feuds and violent reprisals among clans, segmentation of the lineages, and later on, avoidance of military service to the imperial court. Historians believe that many ancient tribal names in Chinese historical records apply to ancestors of the Jingpo: "Qiang," "Sou," "Cuan," "Wu Man," "Xinchuan Man," "Luoxin Man," "Ye Man," "Ochang Man," and "Shantouren." However, early historical records about the affiliation of the people are few and largely conjectural; the records have become relatively elaborate only since the Tang dynasty ( A.D. 618-906), when present-day Dehong was included in the western domain of a highly civilized local kingdom, the Nanzhao State. The geographic location and some cultural traits suggest that Xinchuan Man, Luoxin Man, and Ye Man of the Tang time are probably the ancestors of the Jingpo. In records from the Yuan and Ming dynasties ( A.D. 1206-1628), information about the "Ochang" is very similar to that pertaining to the "Acha," which is an old name of the present-day Zaiwa and Langwo, whom the Dai still call "Acha," "Achang," or "Ochang." Before the Jingpo entered Dehong, the area had long been inhabited by other peoples: the limited fertile valleys were held by the Dai and Han, while the hills were the homeland of the De'ang (Benglong) and some Han Chinese. The dynasties had already incorporated the area into the tusi system, with the Dai as tusi lords. As unorganized, scattered immigrants, the Jingpo could find room to settle only in the mountains. As a whole, the Jingpo were subordinate to the Dai, and they had to pay tributes to the tusi in whose territory they lived. But since the tusi lands were fiefs of the imperial dynasties and the central court also had some direct relations with Jingpo chiefs, the Jingpo were only under the Dai tusi's nominal rule. Well-known as a warlike people, the Jingpo supplied important military support and services to the tusi and the central authority. Some Jingpo chiefs eventually gained the right to collect a "head-protection" fee from one or several Dai or Han villages as reward for their support or services. This pattern of spatial distribution and these sociopolitical interrelations between the Jingpo, Dai, and Han Chinese were maintained until the 1949 Revolution, and they still remain to a limited extent today.