Why would all of us band together?
Simple answer is that as primates humans need the company and support of a group.
We don't always get along but sane people form communities and work out their social problems as they become obvious

The Farmer is the primary focus of all communities because hunting and foraging are not as certain sources of nutrition

Then come the Tradesmen; Mechanics, Blacksmiths, Carpenters and artists of other sorts.

Then would be scout/ foragers who's work restore knowledge of our surroundings and resources available 

Naturally it might resemble a tribal organization with either elected or Ad-hoc leadership