This book explores the importance of public health for understanding the transformation of American power, both domestically and internationally, over the past century. Two pandemics - Spanish Flu in 1918-1920 and Covid-19 in 2019-2021 - provide the context for analysing the actions and responsibilities of the US government both domestically and internationally. It critically examines the provision of health as a public good in the context of the American Century - the application of American power to achieve a democratic, just, and profitable world order under US leadership. By using these two major health crises as book-ends for extending the American Century rubric beyond its usual twentieth century periodisation, the book emphasises the central role that health has played in conceptions of security, state-market relations, and citizenship formation. It critically examines the ways in which race, gender, and class have shaped attitudes to and applications of public and global health as well as how the responses to the threat of disease have brought mixed results, often contradicting the stated goals of social improvement. By reconsidering the American Century through the lens of the political and social struggles surrounding public health, the book provides a unique analysis of US political and social history.