This introductory chapter outlines the problem of social order and the main argument of the book: that the question of what holds complex and diverse societies together has become – and has remained – a philosophical puzzle in modern political science, a presupposition that has been built into our concepts, theories, and normative commitments. Having outlined the argument, the contents and the structure of the book, the chapter then provides a short background for the problem of social order in political science. The chapter recalls how this problem emerged as such in modern social and political discourse in the evolution of the modern concepts of state, nation, and society and discusses how the relations among these concepts provided nineteenth-century political thought with a solution to the problem of social order predicated on a fusion of nationality and statehood.