How did Jean-Paul Sartre try to combine existentialism with Marxism in Critique of Dialectical Reason?

In his work Critique of Dialectical Reason (1960), Jean-Paul Sartre sought to reconcile his earlier existentialist focus on individual freedom with a Marxist philosophy of history.12

Sartre modified his earlier concept of the "project"—previously viewed as an arbitrary choice—by grounding it in the "material conditions of existence," a perspective he shared with Marx. He argued that while individual consciousness remains central, it is conditioned by objective possibilities and must engage in a process of "growing totalization" to form comprehensive human groups.3

Sartre’s synthesis was driven by a critical examination of the Marxist dialectic. He concluded that while Marxism was the essential philosophy of the time, it had become "ossified" in its Soviet form by forcing unique situations into predetermined universal categories. Sartre insisted that Marxism must respect individual freedom and recognize the specific, concrete circumstances of different collectivities. Ultimately, he attempted to identify individual interior freedom with the dialectical necessity of history, aiming to remove alienation from human existence.43