Friedrich Engels, 1880
Socialism: Utopian and scientific

In this extraordinary work, Friedrich Engels, the lifelong collaborator with Karl Marx, describes the greatest accomplishment of Marxism—transferring socialism from the realm of abstract morality, and basing it upon the laws and potentialities of the world as it exists.

He explains the relationship between previously-existing types of socialism, which ultimately considered the reorganization of society as a matter of appealing to the better sentiments of the ruling class, and that of Marxism, which recognizes the material basis for the antagonism between capitalist and worker, and, with the aid of this knowledge, seeks to reorganize society through the class struggle.