The nation-state is a fairly recent historical phenomenon. Human history over the past two to four millennia has been dominated by empires, and the legacies of these empires continues to shape the contemporary world in ways that are not always recognised or fully understood. Much research and writing about European colonial empires has focused on relations between them and their colonies. This book examines the phenomenon of empire from a different perspective. It explores the imprint that imperial institutions, organisational principles, practices, and logics have left on the modern world. It shows that many features of the contemporary world - modern armies, multiculturalism, globalised finance, modern city-states, the United Nations - have been profoundly shaped by past empires. It also applies insights about the impact of past empires to contemporary politics and considers the long-term institutional legacies of the American 'empire'.