" Monogamous marriage comes on the scene as the subjugation of the one sex by the other, as the proclamation of a conflict between the sexes unknown throughout the whole previous historic period. In an old unpublished manuscript written by Marx and myself in 1846 I find the words:

The first division of labour is that between man and woman for the propagation of children

And today I can add: The first class antagonism that appears in history coincides with that of the female sex by the male. Monogamous marriage was a great historical step forward; nevertheless, together with slavery and private wealth, it opened the epoch that has lasted until today in which every step forward is also relatively a step backward, in which prosperity and development for some is won through the misery and frustration of others. "

― Friedrich Engels , The Origin of the Family, Private Property and the State