[...] sooner or later, capitalist property relations become a "fetter," a brake on further development of the productive forces. Society cannot move forward any longer because of the strangehold of private property. Revolution then ensues. The clash between socialized production and private ownership can only be resolved by socializing the ownership - that is, by bringing socialized ownership into harmony with socialized production and setting society on a new course of planned production for human need.
summarizing Marx's preface to A Contribution to the critique of political economy