The first world war is described by the majority of current historians and specialists as a bloodbath, absurd and “useless”, to whose origin almost exclusively resided economic interests and policies of domination of central Empires and powers such as France and England. Without denying the tragedies of the conflict, the essay in question proposes to underline the importance that the Great War had for our country, from the point of view both of the territorial completion of Unity (hence the idea of «Fourth War of Risorgimento», as Pécout has noted) as for the construction of a widespread national and community sentiment, with all the lights and shadows of the case. Finally, the changes brought by the conflict (such as the massive state intervention) and the failure to recognize the decisive contribution of Italy to the victory of the Entente in 1919 will be among the factors triggering the crisis of the liberal state with the subsequent rise of fascism.