Way back then there were all sorts riding around on horseback here and there and so what?
What matters is that this nonsense doesn't.
Tribalism was the world wide norm until the emergence of the Fertile crescent in Mesopotamia
which gave birth to structured agriculture and animal domestication, among other advances.
This led to the development of culture/society having common values and virtues which in turn
led to the emergence of the nation/state.
It was the people of the latter who settled the world and hardly wandering tribesmen!!!!
After the Toba Eruption, it was indeed the wanderers who filled the spaces.
It is a big planet for the estimated 75,000 humans who survived.
When there was plenty of room and resources there was no need for nation states, no need to stake out turf to ensure resources for your band/group/tribe. In fact, running into another group would be a chance to exchange genetics between bands and gain something for your people (band/extended family unit). No doubt such happened.
Structured agriculture came about for a host of reasons, not the least need for a food supply people could control (because when there are too many wanderers, there is no guarantee that the berry bushes won't be picked clean), and because it was efficient.
With agriculture and animal husbandry comes the ability to support a larger population and have concentrations of people who will ultimately form city/states and eventually nations.
But city folks tend to be sedentary, so long as they can. It was (and still is) the wanderers who trade, who find mineral resources, who find the good pasture over the next hill, who pave the way for the establishment of the cities, not the other way around.