The aftermath of the Second World War represented a major turning point in the history of French and European physical sciences. The physicist's profession was profoundly restructured, and in this transition the role of internationalism changed tremendously. Transnational circulation became a major part of research training. This article examines the conditions of possibility for this transformation, by focusing on the case of the summer school for theoretical physics created in 1951 by the young Cécile Morette (1922-2017), just in front of Mont Blanc, at Les Houches. First I show that ultimately it was only thanks to extremely specific and intertwined social positions and dispositions, in terms of class and gender (derived from her socialization as an expected dame de la bourgeoisie), and through the interactions between such social attributes and a dramatic life event, that Morette managed to gather a network diverse, powerful and transnational enough to create this institution. Then, following the first years of this school, I show how it became an international model, paving the way to new articulations between the local, the national and the global scales, even beyond the Cold War oppositions.