Cleavage theory serves as the theoretical starting point for this book’s arguments and analyses. The chapter begins by tracing its origins back to Lipset and Rokkan’s classic work. Specifically, it discusses how this theory was applied to interpret territorial–cultural lines dividing Europe in the nineteenth and twentieth centuries, namely the centre–periphery and rural–urban cleavages. It questions the utility of such traditional cleavages for understanding contemporary developments in political geography. The chapter then reviews how scholars continue to rely on cleavage theory to interpret the socio-political changes reshaping the Old Continent. It surveys the “neo-cleavage theory” literature, showing how globalisation has fostered new socio-cultural conflicts structured around transnationalism. Despite the proliferation of terms—transnational, integration-demarcation, cosmopolitan-communitarian—most conceptualisations capture the same fundamental value-based divide. The chapter argues that existing analyses have focused too heavily on national, regional, or individual levels of this cultural conflict. It therefore advances a framework for investigating a dimension of the new cultural cleavage that has only recently begun to receive the attention it deserves: the territorial–metropolitan one. In introducing this framework, the chapter highlights how political geography within major cities may reveal novel manifestations of this conflict.