Existentialism is when a person is concerned with their existence and their well-being and as a philosophy, it is the theory that humans are in control of their lives and what they do is a matter of free will and NOT by authority. SO, obviously Marx was not necessarily an existentialist, but he was concerned for others whom were Existentialists and began writing the theories of Marxism.
So the main question im trying to ask is: do you consider the Socialist and Communist movements to be completely fueled by Existentialists and does this make it a social revolution or an inner-independence related revolution? because the movements of the past were fueled by a community effort, but were they wanting to help society or themselves and their future generations? were they egalitarianists or existientialists?