People living beyond a state's reach are often not leftovers who never reached civilisation but refugees who fled it: escaping slavery, conscription, taxes, forced labour, epidemics and war. State-making and the history of those who got away are two halves of one story, and wars make states while also making mass migrants.
Mountains, distance and difficult ground once tipped the balance toward self-governing peoples, because states could not easily project power across them. Railroads, all-weather roads, aircraft and information technology shrank that friction so much that escape by distance largely stopped working after the mid-twentieth century.
Tribal identity is less an inherited fact than a decision, often a decision to step out of the counted, settled life that states can tax. What rulers read as instability, scattering and shifting allegiance is usually a survival tactic for staying ungoverned.
States are built on crops that are fixed in place, easy to count and easy to seize, like irrigated rice that anchors labour and grain in one spot. Shifting, scattered cultivation is not a primitive stage but a political choice: it makes a harvest hard to see, measure and appropriate, so it keeps the tax collector away.
Writing serves record-keeping states that tax, conscript and hold people to fixed obligations, so some peoples counted as 'pre-literate' may have dropped it on purpose. Oral custom and history are shape-shifting and can be quietly rewritten as circumstances demand, leaving the state no fixed document to grip.