Primal takes place on a tropical island where three tribes live. Though I'm thinking about expanding it to four or maybe even five and making the island a little bigger. It's still a fantasy setting, but more primitive in nature and none of the tribes believe there is anything that exists beyond their island.
You start off as a little kid that belongs to the Kaimori tribe. The tribe lives by the ocean and tends to have an affinity for water since you're the only tribe that makes boats and travels short distances from the island. They worship a water goddess, regularly fish, and tend to be a little more peaceful than the other tribes in that they don't actively attack anyone except in defense.
The other two tribes are the Umlabo and the Zolopotec (Or just Zolos for short) are more aggressive.
The Umlabo are the biggest tribe and see the whole jungle area of the island as theirs though they make their main home in a more swampy area of the island. They're territorial and tend to have a more "preservationist" mindset since they don't even cut down trees to build huts and just live in the trees themselves. They're also mainly vegetarians and insectivores and view the entire island as something to be worshipped since it provides everything.
The Zolos are the most violent and live in a more barren area on the other side of the island near an inactive volcano that they toss sacrifices in every so often since they worship a fire deity they think lives there. They're also cannibals and often in direct conflict with the Umlabo since they're closer.
Of course there is more but that's the basics. The fourth tribe I was thinking about was the Tanga which would be a beaten subject tribe who live out a pathetic existence of having to provide sacrifices (and meals) to the Zolos every so often.
Life on the island hasn't changed much in many decades, but naturally your protagonist is lucky enough to live during interesting times. So tribal warfare on a mass scale, hurricanes, tribe restructuring, belief questioning and possibly even a few foreign visitors to your isolated island are all going to play a part.
While this all probably still sounds like it will lend itself to a story on the longish side, I'm hoping it won't since I still have the overall idea of this is a primitive island setting and people just don't tend to die of extreme old age. So no living to be over 100 years old, at best you might get to "year 60" and you start off at "year 10" at the beginning of the story anyway.