There is indeed a succession from simple hunter-gatherers to complex integrated polities, but different regions have achieved different levels of complexity due to a combination of historical factors and environmental conditions, rather than the lack of 'cultural capacity'. We now use less value-laden labels for these sociopolitical formations. Egalitarian hunter-gatherers, usually living in small mobile groups. Egalitarian refers equality in status. Excessive differences in status rarely occur, except in sedentary hunter-gatherer societies, where it was possible to accumulate wealth and power in areas of rich resources.
Some individuals perform formal roles of leadership and decision-making.
Leaders may play a more permanant role in these larger groupings, but they are chosen based upon their personal characteristics, rather than by heredity. Institutionalized leadership roles exist in societies with larger and more complex settlements in regions with higher population densities. Permanant leadership divides the society into the ruling family and retainers, versus the rest of the society. A state becomes an Empire when it becomes powerful enough to control other states. For example, the Roman Empire.