Saoralba hit the nail on the head!
Local micro-climates, rain-fall, soil types, drainage, temperatures, etc. define how "agriculturally successful" a clan, tribe, nation, commonwealth can be and that agricultural success defines how large the tribe can grow.
More successful tribes grow in stature (physical height and weight) and eventually absorb neighbouring tribes. As they continue to succeed, the most successful tribes eventually elect kings. After a few centuries of ruling, Royal
Families get all pompous and claim their "god-given right to rule."
But it all started with the choice made by which family settled on the best soil.
Human society evolves from lone hunter, to immediate blood relatives, to extended family, to clans, to tribes, to principalities, to baronies, to fiefdoms, to Royal kingdoms, the empires, to nation states, to commonwealths, to European Economic Communities, etc. based on how much wealth a group can accumulate.
But at the basic level, humans still need smaller, local neighbourhoods, teams, congregations, political tidings, etc. where they can see the face of power.
For example, Somalia is populated by a variety of "clans" because that poor, arid country can only support a low population density. Because Somalia was never a wealthy country, it could never collect enough taxes to fund a centralized nobility or standing army or elected parliament or coast guard or government bureaucrats. In short, Somalia is too dry a nation to pay for a central government.
OTOH up on the Etheopian Plateau they get enough rain-fall to support enough agriculture to feed themselves and generate small surpluses, surpluses large enough to support an idle Emperor who lived in luxury.
Granted, some prejudiced people may use the term "tribe" to put down other groups "less evolved" than them, but those "tribes" may have evolved to the maximum carrying capacity of their land and simply cannot support kings.