This chapter examines the role of the Opium Wars and great power conflict between Britain and China within the context of drug control. Within the Opium Wars, the foundational elements for the coming global drug control system were laid. These included straining bilateral relations between great powers as well as the emergence of nationalist and moralist coalitions of diplomats and missionaries driving ‘reformist’ agendas globally. The first international treaty, the 1912 International Opium Convention, aimed to create reciprocal state responsibilities for limiting the flow of mind-altering drugs. After World War I, the new multilateral drug control system was quickly absorbed by the League of Nations. However, the US’ simultaneous interest in the issue and unwillingness to join the League of Nations proved complicating. Throughout the 1920s and 1930s a whole series of treaties and institutional changes gave the system regulatory shape. The League Opium Advisory Committee, precursor to the UN Commission on Narcotic Drugs (CND) ultimately sank. The enforcement and monitoring bodies, survived and fled Geneva for the safety of Washington DC. The chapter concludes with a brief introduction to the main diplomats of the wartime era, most prominently, Harry J. Anslinger.