Grounded in multilingual governmental and private sources, this dissertation redefines twentiethcentury China beyond the territorial boundary of the Chinese nation-state. Even though China and Indonesia are not neighboring countries with geographic borderlines, the existence of approximately 2.5 million ethnic Chinese in Indonesia gave rise to an invisible and porous social frontier that could be transgressed more easily and oftentimes accidentally, especially during a period when the Chinese Communist Party's  regime  legitimacy  was  challenged  by its Nationalist rival.  At  the  level  of  the  Chinese  state's  relationship  to  the  overseas  Chinese,  Chinese  political elites used transnational migrant networks and the global circulation of media to rally popular support  and  affirm  political  legitimacy.  At  the  level  of  the  overseas  Chinese's  relationship  to  the   Chinese state, the ethnic Chinese were active participants in civic campaigns launched by the proChinese Communist and pro-Chinese Nationalist factions in Indonesia. Both sides claimed that all  ethnic  Chinese  owed  their  loyalty  to  China's  sole  legitimate  center-Beijing according to the Communists or Taipei according to the Nationalists. At the level of state-to-state diplomacy, this continuous politicization of the ethnic Chinese shook the foundation of the Sino-Indonesian strategic partnership.  The  ethnic  Chinese's  daily  social  and  political  practices,  as  well  as  their   ideological beliefs and emotional ties, limited high politics between the Chinese and Indonesian Governments. By connecting transformations in state-diaspora, diaspora-state and state-to-state relations, and by combining theoretical insights from the China-centered approach, overseas Chinese studies, transnationalism and diplomatic history, my dissertation builds a new conceptual framework for a transnational China that is vigorous and dynamic not only within its geographic boundaries but also beyond. Ultimately, I argue that the global emergence and embrace of the People's  Republic  was  not  one  historical moment within China but a set of temporally and geographically expansive processes that involved the Chinese  Communist  Party's  adaptation to a new relationship with the overseas Chinese, a new type of political struggle against its old rival the Nationalists, and a new international geopolitical environment.