During the first XXth century, war, violence, forced migration, man-made famines, and epidemics were responsible of tens of million deaths. They left deep scars in the survivors, altered the equilibrium between genders and between generations, and affected in multiple ways the European demographic system, including the geographical distribution of the population. The collapse of multinational empires led to the identification of the State with the nation, and of the nation with an ethnic group, and bred an intolerant hyper-ethnicism, culminated in ferocious episodes of ethnic cleansing and genocide. This book is about the victims of these unrests, caused by political choices, and it carries out an analysis of the elements that led to the convincement that States could manipulate the number, the structure and the distribution of populations.