During the Second World War, the experience of Sartre and others in the French Resistance to the Nazi occupation of France emphasized political activism as a form of personal commitment. This political dimension was developed in Sartre's later trilogy of novels, Les Chemins de la Liberté (The Roads to Freedom) (1945–1949), which concern a vicious circle of failure on the part of a thinking individual to progress effectively from thought to action. Finally, for Sartre, political commitment became explicitly Marxist.
In 1945, Sartre gave a lecture in New York that was printed in Vogue in July of that year. In it he recast his prewar works, such as Nausea into politically committed works appropriate to the postwar era.
Marxism was not, in any case, always as appreciative of Sartre as he was of it. Mattey describes their objections:
Marxism was a very potent political and philosophical force in France after its liberation from the Nazi occupation. Marxist thinkers tend to be very ideological and to condemn in no uncertain terms what they regard to be rival positions. They found existentialism to run counter to their emphasis on the solidarity of human beings and their theory of material (economic) determinism. The subjectivity that is the starting point of existentialism seemed to the Marxists to be foreign to the objective character of economic conditions and to the goal of uniting the working classes in order to overthrow the bourgeoise capitalists. If one begins with the reality of the "I think," one loses sight of what really defines the human being (according to the Marxists), which is their place in the economic system. Existentialism's emphasis on individual choice leads to contemplation, rather than to action. Only the bourgeoise have the luxury to make themselves what they are through their choices, so existentialism is a bourgeoise philosophy.