For a really long time, humans lived in small groups as hunter gatherers where, for obvious reasons, food had to be either hunted or gathered.
One day, agriculture happened and humans no longer have to hunt or gather stuff. They can grow all the food they need (mainly potatoes?) out in their own backyard. With this, humans can now afford to live in bigger groups.
As the group gets larger and larger, so does the farm. So large, in fact, that a small city or town was born. And with such a (relatively) large population where the farmers can supply all the food the community needs, some people started specializing in other fields (like politics?) and dividing themselves into classes (like peasants and aristocrat?).
The discovery of agriculture was definitely a fun time for some people, but not so much for everyone else. Back in the hunter gatherer days, we lived in small groups where everyone was more or less equal. But once agriculture came, once we have a method of storing value (i.e. food), it became possible for some to get rich and start hoarding power. Which is probably what resulted in class divide and all that stuff.