Who does Marx say that the history of struggles is between? Give one specific example that he cites from The Communist Manifesto.

In the first chapter of the Communist Manifesto, Karl Marx writes that the history of struggles is between people of a different class. Specifically, this is a struggle between "the oppressed and the oppressing" and Marx provides several examples: "freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman." 

If we take one of these examples, like the lord and serf, we can put this into context. In the Middle Ages, a serf was a unfree peasant who lived and worked on his lord's land. Under the system of feudalism, the serf could not leave this land, could not marry without his lord's consent and had to dedicate much of his labour to producing food specifically for his lord's family. This, argues Marx, is an exploitative relationship because the serf is economically subservient to his lord. It is the lord who benefits from this relationship through his control of the means of production (the land) while the serf lives in bondage. 

Historically, feudalism began to decline in the 1400s, brought on by new economic conditions after the Black Death of 1348. As a result, serfdom died out but, according to Marx, the exploitation of workers continued, just under a new name.