The contribution analyses the centrality of the piazza Fontana massacre in the dynamics of development of the political system. The Republic experienced a break that marked the transition from the Golden Age to the crisis of the 1970s. The link between the internal framework and the international dimension takes on the characteristics of an observation point to follow the transformations of institutions, parties, political cultures. The overflowing of political violence marks a point of no return in the social and generational framework.