The study of how party systems are structured across territorial lines is a crucial research topic for political scientists, and one fraught with consequences for the political system and the democratic process. Cleavages, Institutions and Competition addresses this topic and raises the following questions: How has vote nationalisation evolved in Western Europe during the past fifty years, and which factors account for its variation across Western European party systems? This book answers these questions through a macro-comparative perspective and an original empirical research based on 230 parliamentary elections in 16 countries between 1965 and 2015. The result is a far-reaching understanding of the constellation of factors involved in the process of vote nationalisation, including macro-sociological, institutional and competition determinants.