From the summer of 1914, European societies seem brutally seized by war and, as a consequence, seized by the State. In the name of the State, millions of men enrolled in the armed forces are to fight one another. Bodies, minds and resources are subjected to a gigantic "mobilization", a contemporary word still used by historians. A hundred years later, when all the warring States, as well as the States that were born from the conflict, are launching ambitious commemorative programs, the moment seems well chosen to study how the State wages war and, in return, how war transforms the State. As part of this vast topic, this international and multidisciplinary (history, political science, sociology) conference will address the invention of the War State, from the perspective of all the processes through which the event has – or does not have – an impact on the organisation, actions and conduct of the public power. The aim is to identify potential changes or limited adjustments, but always within situations of transition born from the conflict. Is the intensification of the State's hold on society immediate or gradual, continuous or discontinuous? Are there slower phases, failures? Is it paralleled with a loss of influence in other areas? Is it possible to detect forms of resistance or avoidance, while refraining from all generalizations and risky extrapolations? Questioning the process of nationalisation of European societies is one of the challenges of this multidisciplinary work, which is widely open in space and time around the 1914 key date. Composed of well-defined surveys, the book falls within a social perspective of war, and allows us to question what seems obvious, at least in France: the spectacular capacity of the State to mobilize, almost overnight, an entire society.