Three hundred years after its appearance Christianity was the recognized state religion in the Roman World Empire, and in barely sixty years socialism has won itself a position which makes its victory absolutely certain.
Friedrich EngelsPeople have learned by bitter experience that the "European fraternal union of peoples" cannot be achieved by mere phrases and pious wishes, but only by profound revolutions and bloody struggles; they have learned that the question is not that of a fraternal union of all European peoples under a single republican flag, but of an alliance of the revolutionary peoples against the counter-revolutionary peoples, an alliance which comes into being not on paper, but only on the battlefield.
Friedrich EngelsWhat is Communism? Communism is the doctrine of the conditions of the liberation of the proletariat. What is the proletariat? The proletariat is that class in society which lives entirely from the sale of its labor and does not draw profit from any kind of capital; whose weal and woe, whose life and death, whose sole existence depends on the demand for labor.
Friedrich Engels