Regarding ancient times when nomad tribes abounded, people would choose to become sedentary (establish their lives in one place) once determining the environmental conditions, security, and food availability were suitable for their taste.
Nomad tribes are compelled to hunt and gather on their endless journey for sustenance. Once learning agriculture and animal husbandry techniques to apply in a suitable environment, these tribes are able to settle in one place and concentrate on the prosperity of their new civilization.