Peng Kun, Shi Yuqing, and Ke Shuxun were awarded the title of ＂three Elders of Frontier Defense＂ by the Yunnan provincial government and were well known by native people for their crucial role in the formation of the Yunnan- Burma frontier from the 1870s the 1940s. The Peng family established Shuangjiang County out of the earlier ＂Five Buddha districts＂ system, which was controlled by the indigenous Lahu (Luohei) people. The Shi family weaved a marriage network with other powerful families and acted as their representatives to control local opium markets and trade with trades in the Wa Mountains. The Ke family implemented a political reform known as ＂dual govemance by chieftains and officials＂ in Sipsongpanna, south of the Lahu and the Wa Mountains. These three powerful men and their families actively participated in the transformation project of the Qing and Republican states over several decades, and secured their own political, economic and moral interests during the course of negotiations among China and the British and French colonial powers over the drawing of a border between China, Burma, Vietnam and Laos. Frontier politics, which was among the central issues in the construction of Chinese nationalism, was deeply affected by native agency. Native involvement allowed political reforms to the system of native chieftains to continue at the same time as the Chinese state was transformed at to a modem nation- state through the demarcation of borders. Through their influence, new economic patterns of opium and tea trade took the place of traditional agriculture and reshaped local society; the presence of new immigrants led to identity change as they became ethnically non- Han and in some cases middlemen between Han elites and other local ethnic groups. As frontier politics and identity politices interacted, the Qing system gave way to the warlord politics of the Republican period. Local agents of the state participated not only in the construction of the modem state but also in the project of border demarcation. This paper integrates ethnic politics as well as the importance of the local ecology into our understanding of the history of China's southwest frontier.