“Freeman and slave, patrician and plebian, lord and serf, guild-masterΒ and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary reconstitution of society at large, or in the common ruin of the contending classes.”
http://www.anu.edu.au/polsci/marx/classics/manifesto.html