NOTE: I will rename "Amazon" to "Amozan" to avoid confusion with the South American region. The world of Noah, the setting for my current fantasy story, has no extensive empires and very few if any large cities; pretty much everyone lives in primitive Copper/Early Bronze Age tribal societies that frequently war against each other. The world's human inhabitants can be sorted into three races: the white Japhethites of the temperate north, the tawny Shemites who roam the central deserts, and the black Kamites of the tropical south. The Japhethites and Shemites have patriarchal cultures whereas the Kamites are matriarchal in that women wield political and spiritual authority (though men still do most of the fighting and hunting). What I want to ask right now is whether I should add a few civilized cultures to the world. The reason is that one of my protagonists is a Japhethic pirate from Asgard, but I don't know if piracy would likely develop in a wholly primitive setting since there would be less inequality in wealth than in a setting with more advanced civilizations.
Variety is the spice of life. The more differences the better the competitions the more wealth. Relying on three races makes it rather tight for money if you see what I mean. I would say you need to thrown in a bit more less obvious cultures for mystery and suspense. It would be very boring if the world revovlved around 3. you would have seen it and done it all. So I would yes if you want a wealth of actions in your story you would at least to refer to other cultures and civilisations to make the book come alive with cross culture references which will add character to the book. The more the merrrier they say May I ask you why you called it barbaric if they are going to be civilised?
The original idea was that everyone in the world would be a "barbarian". But like you said, since variety is the spice of life, I'll add some civilized cultures in addition to the barbarous ones.
I have no idea where you got that idea. Piracy has existed pretty much as long as boats have. And 'primitive' societies can have inequality of wealth just as much as 'civilized' societies do. Like the guy who owns 5 horses while most people only own one. The biggest concern I'd have with you adding more advanced civilizations is explaining why the other groups aren't that advanced. Most societies tend to be roughly equal in technology to their neighbors. Partly out of trading, partly out of espionage and military preparation (it sucks to be using spears against guns) and partly out of getting inspiration ('I never knew you could do that! Given that it's possible, I bet you'd do it this way.'). So there'd have to be a pretty good explanation for why they aren't the same technological level.
I suppose the answer to your question depends on what you want to do with your story. If it's a take based around warring cultures, political conflict etc then 3 races/nations will be restrictive. Of it's a tale of individuals within one if the races with the nations as a backdrop then far less so. You could have other races or civilisations across the sea, allowing marked contrast in cultures (given they developed in isolation) or could have more races in the past thought to have died out, or magical races existing in parallel, or secret, or underground. Suppose depends on your plot direction and what sub-genre you're aiming for.
Hm, I'm not sure that it makes sense to have naval piracy in the world where there is no naval commerce in the first place. And to have commerce, you need inequality of wealth both on a regional and local level. In our world, trans-Atlantic piracy never existed prior to colonial era! You need to have naval contact between your cultures, and then you need it to be extensive enough to actually have any reason for piracy. Think about the economy of your world - it's the most boring thing in world-making, but it's essential if you want it to make sense. What does your pirate steal? Is he after raw fish, or rare spices, or gold? You need to put something on those ships your pirate is gonna board.
