This dissertation is a history of religion on the “peripheries” of the modern Chinese state, the Japanese wartime empire, and the Tibetan Geluk Buddhist world. Using a transnational history approach, the project uses multilingual source materials collected from archives located in China, Japan, Taiwan, and the United States and challenges traditional disciplinary categories in postwar Religious Studies and Area Studies. Focusing on interwar Inner Mongolia and Manchuria, an understudied region within the postwar academic disciplines of Buddhist Studies and Areas Studies, my dissertation explores the history of transnational Buddhist networks in the region that both supported and challenged the nation-building and empire-building efforts of modern China and Japan (1912-1949). The specific temporal scope of this project is between the fall of China’s multi-ethnic Qing Empire in 1912, and the retreat of the Chinese Nationalists and their Republican government to Taiwan in 1949 after their defeat in the Chinese Civil War. This period also saw the rise and fall of the Japanese Empire in 1945 and the establishment of the People’s Republic of China under the Chinese Communist Party in 1949. During this period, Inner Mongolia and Manchuria, the continental regions of Northeast Asia and the “frontiers” of the Qing Empire, became the new “borderlands” that both the modern Chinese Nationalist Republican State and the expanding Japanese Empire competed to take control of. The two regions were administratively disciplined through the laws of Republican China (albeit often nominally) and effectively occupied by Japanese settler colonization as well as military and industrial annexation. Both regions also eventually saw the births of two modern states, the states of Mengjiang United Autonomous Government (1939-1945) and Manchukuo (1931-1945), although both are often referred to as “puppet states” of the Japanese Empire. At the same time, local Buddhists, both monastic and lay, in Inner Mongolia and Manchuria positioned themselves differently and beyond the spatial and temporal limits of the modern nation and empire. Using Buddhist networks connecting Manchuria in the East to Tibet in the West that have existed since the eighteenth century, Buddhists negotiated agency and mobility in this volatile interwar period marked with various crises of modernity. In this dissertation, I identify three types of Buddhist networks operating in early twentieth-century Inner Mongolia and Manchuria, namely, 1) a transregional Inner and East Asian monastic and intellectual network formed in the Qing period, 2) border-crossing Buddhist networks informed by old lineages in Inner Asia and new patronage in modern China that responded to Buddhist sacred geography, historiography, and apocalyptic time, and 3) transnational networks paved by Japanese Buddhists and Mongol monks that promoted an Esoteric Buddhist Pan-Asianism in the Japanese wartime empire. I argue that these Buddhist networks not only engaged in various overlapping nation-building and empire-building projects in the interwar geopolitical landscape of Northeast Asia, but they offered cross-border access to Buddhist and non-Buddhist individuals to exercise agency and mobility to extend and maintain landscapes of their own that challenged the spatial-temporal orders of the modern nation-states and empires.