Tribal world needs tribal mentality! You did say this was not about those massive borders and all that, so why focus on far men and wait until things develop? The fun of this RP would be the down to the ground tribal interaction.
I'd say, GM, join in or at least create events so people can interact more. The world is wild and even a pack of wolves can be a danger to these tribes.
Anyway, my NS.
Tribe Name: Hu'pira
Demonym: Ex. Hupiran
Population: 300~
Government Style: Council of priestesses. People elect a "good hunter" when there is trouble, this person gets control of the warriors.
Religious Beliefs: The tribe believes there are many underwater gods and that each tribe descends from a different one. The Hupiran people was born from Minana, the bastard child of one of the sea gods with an earthly giantess, because of this the goddess was never accepted into the sea and had to live in a swamp. When gods started to make people to live on the land Minana did too, but meanwhile the other gods could give their children the coasts, the fertile plains and the metal rich mountains the Hupiran goddess could not offer them anything but the swamps, yet the Hupiran were good childs and they did their best to live a good life and honor their mother.
Location on the Map: That swamp like area on the southeast of Altara
History before the Collapse: The Hupiran people lived on a great swamp, the trees there were so big that a whole family could live in a tree hollow. The swamp was so big that no sea people rarely dared to go deep within it, there was one exception though, a vile vile tribe once discovered a path to the motherland and seeing that the Hupiran had no riches they dared to ask for the last thing we had, our children! We battled at first but then came Vuz the betrayer, the son of a priestess who was enchanted by the riches of the vile people. Not only he took the children away but he also went against our mother.
Survival Legend: The vile people finally went too far and angered the gods, at first the swamp was fine, but then the water became odd and slowly became salty, that was when the elders realized the land was sinking. The people were not like the sea child so they didn't know how to escape, slowly the water went up and up and finally the whole swamp had sank, the people only survived on a cut down logs of the great tree, but having no way to sail away they were bound to starve. That was when Minana showed herself, she took pity of her child and decided to at least not let them starve or drown, so she ate the trees with all the people inside.
For a year the people stayed inside the stomach of the goddess, they were deep in the darkness but they never felt lost, most of the trees were digested, three were spit out in the new lands.
History Since: The goddess had expected the people to leave her and to become sea people like the others, but as soon as they stepped in the new land the tribe searched for a swamp, none was as beautiful as the one Minana made, but they settled on one. There the tribe went back to live their typical life, this time however they were way more weary of foreigners and didn't want this land to sink too.
Other: (Eventually will add more)