This book explains how and why ethnicity changes across time, showing that, by altering the basis of economic production from land to labour and removing people from the 'idiocy of rural life', industrialization makes societies more ethnically homogenous. Using large-scale datasets that span the globe as well as detailed case studies ranging from mid-twentieth-century Turkey to contemporary Botswana, Somalia and Uganda, as well as evidence from Native Americans in the United States and the Maori in New Zealand, the book provides a new framework to understand the origins of modern ethnic identities.