Since the end of the Second World War, separatist nationalism and social mobilization have received great attention from social scientists. Both have attracted the interest of scholars who have since engaged in endless disputes over methodologies, theories and paradigms. Separatist Nationalism, understood as the nationalism that aspires to transform from a non-sovereign nation into a sovereign nation-state has from its conceptualization, been on the rise. Spain, a nation composed by 17 autonomous communities and strongly influenced by the country's historical past has in the latest years been witness to what separatist means, autonomic claims and self-determination movements represent in the splintering of a nation and its peoples. The unsettling sundering the Spanish nation is undergoing has prompted the need to address this matter, in the means to better grasp and contribute to the understanding of the Spanish nation and its rising issues. This study, framed into 3 chapters, encompasses a critical examination of the course of historical events and an address of nationalistic and constitutional development, in the rise and struggle of separatist-nationalism.