This chapter examines China’s diplomacy during the Republican era from 1911 to 1945, with a focus on the Beiyang government’s approach to the Versailles Peace Talk and the Nationalist government’s confrontation against Japan. It argues that both governments’ decision-making in foreign policy were driven primarily by security, especially territorial integrity, but also quite significantly by the political leadership’s need to preserve political legitimacy in the face of strong nationalist currents. As evidenced in the Nationalist government’s subjection to its anti-imperialist rhetoric in its Japan policy, ideological factors still retained a noticeable influence in shaping the political leadership’s decision-making processes.