As Empires Expand

As empires expand through traditional means of conquest, deception, or bullying become increasingly diverse, complicated, complex, and spread out, the costs of maintaining what's present increases exponentially, as does the cost of expanding it further. What reduces this expansion of costs includes receiving voluntary support from all populations, union in a common goal or vision, and an effective, efficient, and inclusive state and state bureaucracy aimed at improving the actual quality of life for those in the empire's boundaries. If there isn't consent, if there isn't union around a common set of goals and visions, or the state is capricious, inept at providing quality public services at appropriate scales and at value-cost, and/or is exclusionary to others in the territory, the costs of maintaining the empire increases exponentially the more these polices are emphasized.

Wikipedia, accessed 11/2/2017

Consider the Mongol Empire.  Chinggis Khan grew the world's largest land empire in history.  Yet he also managed to govern well enough, and establish effective enough institutions to enable the empire to last some 700 years across Asia.  It buckled under disunity incited by succession challenges, the failings of its monarchic-like institutions, and as newly risen former peon powers rose up and successfully challenged Mongolian suzerainty (indicating that voluntary consent was not the reason why people paid homage to the Khans).  Indeed, if one looks at history comparatively, we can see that the reasons behind the Mongol Empire's fall are similar to the declines and collapses of most, if not all overly-hierarchical, overly-concentrated political unions brought together by force and/or deception and not through a truly consensual union between the partners.  Yet these anti-social structures have been what have dominated human societies and human social dynamics since the beginnings of recorded history.

Indeed, any empire or social unit can act as a template for analytical study.  There are many ways to study each social unit and its relations within itself, other groups and people, and the ecosystems they inhabit to infer how we can make better choices in our present time, and to understand ourselves more accurately as a species in a universe.  By looking at the relative costs of maintaining and managing different social systems, we can understand how to better shape our current institutions, and understand the limitations of those institutions.

Source (as a repository of academic sources on the Mongol Empire):

https://en.wikipedia.org/wiki/Mongol_Empire