It seems fairly certain that they once lived with the great bulk of their linguistic congeners, the Athapascan-speaking tribes of north-central Canada.
It is not possible to reconstruct the social and political structure of the Navajo people at the time they first entered the Southwestern region. As a semi-nomadic hunting and gathering people, they probably moved in small, male-dominated extended family groups, each guided by a head man owing allegiance to no particular other group. The Navajo at that early period were probably bound to each other by no ties other than speaking a common language and sharing a common culture and genetic kinship.
Almost certainly the "Navajo" tag came into Spanish from one of the Pueblo peoples of New Mexico early in the 17th century when the ancestors of today's Navajo people first came to the notice of European settlers along the Rio Grande Valley. Like other southern Athapascans, the Navajo found Spanish settlers a very tempting target for economic raiding. The horses that Spaniards introduced into the New World constituted a particularly attractive sort of precious good for organized thievery.
Navajo women could divorce her spouse during historic times quite simply. She who controlled the mutton stew pot controlled the household.. Male economic raiding and female property control and inheritance rules are bound to come into conflict. The male Navajo raiders from time to time brought home war captives. Now no warrior in his right mind would bring back adult male captives to a home camp. War captives brought home, therefore, consisted of either young children who would be reared as Navajos, or sexually attractive adult Spanish or Puebloan females.
While Navajo warriors carried on economic and retaliatory raiding against Puebloan and Spanish settlements, their wives and daughters continued to tend to the sheep flocks. These continued to grow in numbers, so that this period saw the Navajo people expand their grazing territory appreciably toward the West.