If the proletariat during its contest with the bourgeoisie is compelled, by the force of circumstances, to organise itself as a class; if, by means of a revolution, it makes itself the ruling class, and, as such, sweeps away by force the old conditions of production, then it will, along with these conditions, have swept away the conditions for the existence of class antagonisms and of classes generally, and will thereby have abolished its own supremacy as a class.
Signet Classics edition of The Communist Manifesto, by Karl Marx and Friedrich Engels, with an Introduction by Martin Malia and a New Afterword by Stephen Kotkin, pp 93-94