The philosophy of Jean-Paul Sartre started as a reflection about the consciousness and the self, questioning about the possibilities of the individual. Suddenly, the WWII caught all these possibilities, forcing the young bourgeois Sartre to convert to the reality of his time. His life, his thoughts, his philosophy changed. Since then, History has become a sort of focal point. The relationships between the individual and the society, the man and the Epoch, the historical action and its practical results were the centre of Sartrean reflection. All these ideas were destined to constitute the mature Critique of Dialectical Reason. This paper wants to show how much the historical changes that were at the core of European society at the end of ‘30s led to the ethical turn that occurred in the ‘40s in Sartrean philosophy, which brought Sartre to describe the possibilities of the actions of the mankind, namely the History and its horizons. This movement discloses an ethical side of Sartre that is generally undervalued, but that could surely give some suggestions about the insertion of the Ethic in the History. The central question of this paper concerns the roots of the historical action, which are situated in the ground of Sartrean ethical reflection. To act historically is to act socially, and to act socially is, inexorably, to act ethically.