"This book presents a theory to account for why and when politics revolves around one axis of social cleavage instead of another. It does so by examining the case of Zambia, where people identify themselves either as members of one of the country's six dozen tribes or as members of one of its four principal language groups. The book accounts for the conditions under which political competition in Zambia revolves around tribal differences and the conditions under which it revolves around language group differences. Drawing on a simple model of identity choice, it shows that the answer depends on whether the country is operating under single-party or multi-party rule. During periods of single-party rule, tribal identities serve as the axis of electoral mobilization and self-identification; during periods of multi-party rule, broader language group identities play this role. The book thus demonstrates how formal institutional rules determine the kinds of social cleavages that matter in politics."--BOOK JACKET.