This dissertation reconsiders the political and ethno-cultural frontiers of North China, taking as a case study a group that thrived in the Eastern Intermediate Zone (Hebei-Liaoning-Rehe border zone) known as the Qai or Tatabï in Turkic sources, as the Kumak Qai (Kùmò Xī 庫莫奚), and later, just Qai (Xī 奚) in Chinese sources, and now Tatayar in Kitan sources. The dissertation argues against the existence of a strict borderline between southern sedentary agrarian polities and northern nomadic pastoral polities by documenting the development of early polities in the region, highlighting the transition from “Big Man” polities based on the strength of individual personas to the development of hereditary houses in the model of steppe and Chinese hereditary empires from the second century BCE to the tenth century CE. The story of state formation in the region is told through the combination of historical ecological data from the region (modern-day Ningcheng county, Inner Mongolia), traditional Chinese historical accounts (termed “pseudo-ethnographies”), and the incorporation of newly accessible Kitan language sources. The historical politics and ecology of the region are complex, and the Qai were not horse-riding herders as some of the pseudo-ethnographies suggest; they made use of the environment through the cultivation of crops, the raising of livestock, hunting by foot mountain forests, and other ways. Under the Kitan Liao (907-1125), Qai identity was preserved, reemerging with the establishment of the short-lived Great Qai State in 1123, but the Qai Princes of the Liao and their staff, appointed by the Kitan, did not represent Qai interests. New developments in the Kitan language sources reveal the Qai autonym, Tatayar, and the title of the Qai leaders, qaghan, confirming that the Qai were an historical community with hereditary titles in use prior to the Liao. Geographical boundaries do not necessarily define ecological boundaries. The cycle of polity formation shifting between “Big Man” polities and hereditary monarchies ending with the rise of the house of Yêrud (Yélǜ 耶律) of Liao demonstrates that foreign influence catalyzed state formation, yet ethnicity did not determine political loyalties.