Clans

Quote from the dev:

In essence, every polity has factions. A tribe is a type of polity and a clan is a type of faction. In a tribe, the most dominant clan is the one that takes decisions for the whole tribe (opening up, allowing splits to happen, etc) When a tribe initially appears it starts with a single clan which is by default the dominant one. But as the tribe grows, the "administrative cost" of maintaining the tribe under a single clan grows and the clan might be forced to split. This is a mechanic that will later be reworked since clans IRL do not split because of "administrative issues", they split simply because large families grow apart. When new clans appear, they take up some of the administrative load of the tribe, allowing it to grow larger. This percentage of admin load they take is proportional to their level of influence within the clan which fluctuates over time. A non-dominant clan with a large influence, but not enough to take over the tribe, might have two choices, demand influence from the dominant clan, or split from the tribe to form it's own tribe. Both decisions can be countered by the dominant clan, but in doing so, they undermine their own authority, leading to further attempts from weaker clans to take over or to split