There is a Lisu tradition that their origins lie in the eastern Tibetan plateau. The Lisu are mentioned among the "Southern Barbarians" (of mountainous Yunnan and Szechwan) in the early Chinese histories and annals such as the Man Shu (ca. A.D. 685). The Chinese regarded them as a lesser branch of the Han, to be pacified and assimilated. This explains the derogatory names applied to them and the two trends discernible in Sino-Lisu relations: peaceful coexistence, cultural exchange, trade, and intermarriage on the one hand, and constant small-scale warfare, raids, kidnappings, banditry, enslavement, suppression, and rebellion on the other. The Chinese exchanged salt, iron, silver, and foodstuffs for beeswax, bear gall, stag horn, hides, medicinal herbs, and coffin planks. In areas closer to Chinese settlements, such as Tengyueh and to the south, Lisu were taxed, corvéed, and appointed as headmen ( tussu ) and government officers ( tumu ), perhaps as early as the Han dynasty, and certainly by the Ming. The system seldom worked well, and there were numerous grievances. After the formation of the People's Republic of China, army units and government cadres arrived to administer Lisu areas, and the Nuchiang Lisu Autonomous Zhou and other autonomous areas were formed. The abolition of slavery, land reform, and cancellation of debts were decreed in 1956. Chinese influence on Lisu culture, already considerable before 1949, has accelerated, as evidenced by the virtual end of opium growing, the introduction or extension of double cropping, manuring, irrigation and terracing, new tools, roads, bridges, medical centers, schools, economic diversification, the organization of mutual aid teams, cooperatives and communes (and their subsequent abandonment), and the development of political consciousness evident in Lisu cadres, soldiers, and Communist Party members. These changes caused great stress, particularly during times of radical change such as the Great Leap Forward and the Cultural Revolution, when "local nationalism" was criticized and rapid movement toward socialism demanded. During the lulls in Communist fervor, a continuity with the past can still be discerned: the vast majority of Lisu are still small-scale agriculturalists in remote mountain villages with few modern amenities. The movement of Lisu peoples south and east into Burma, India, and Thailand may have been related to the development of opium growing and worsening relations with Chinese administrators in the nineteenth century. Chinese pacification measures in the late nineteenth and early twentieth centuries caused large-scale movements of Lisu into Burma, and subsequently Thailand and India. Oral traditions of the Lisu in Thailand indicate that the first families arrived there from Burma between 1900 and 1930, motivated by the search for good high-elevation opium lands and a wish to escape unsettled conditions in China and Burma. The Lisu have been described as a "fine" people: robust, independent of spirit, and excellent warriors. They are also very adaptable and quick to learn the languages and ways of their neighbors. Some, especially in Myanmar and Thailand, have even intermarried with Chinese, Lahu, and Kachin, recognizing a fictitious equivalence of Lisu clans and lineages with those of neighboring ethnic groups. Chinese operate stores or caravan routes in Lisu villages, and the Lisu patronize local markets. Lisu have served in the British Burma army, the People's Liberation Army, and the Thai Border Patrol Police. Christian and Buddhist missionaries among the Lisu have not been very successful.