Oligarchy: rule by the most vicious few over the more innocent many; the default way of organizing societies.
There are in practice three kinds of government: naked oligarchies, covert oligarchies, and non-oligarchies which tend to degenerate into oligarchies. The explanation of why this is so has at least three levels, each deeper and broader than the next. At the highest, most apparent level, there is what Robert Michels called in 1911 the Iron Law of Oligarchy, which is that the centralization of power is the most efficient way of organizing large groups. Bureaucracies form as control needs to be specialized and delegated, and as the bureaucracy grows, higher and higher levels of command need to be put into place to avoid a regress to anarchy, whereupon those near the pyramid’s apex tend either to be corrupted by the greater power they acquire or to have been sufficiently vicious in advance to have successfully worked their way to the top of the hierarchy, wining out against cut-throat competitors.
More broadly, the most stable social structure in species whose members live in large groups, including birds, fish, and primates, is the dominance hierarchy in which power is centralized in a minority of alpha males or females who maintain a social order by rigorously enforcing rules of which members enjoy such benefits as privileged access to food or to mates. Oligarchy in human societies is just our form of the dominance hierarchy, which is to say that the underlying structure of our myriad social systems is naturally selected.
Deeper still, the inevitability of oligarchy and the injustice entailed by any such gross inequality have Gnostic flavours, revealing the existential, mythical status of our ultimate position within nature as accursed, imprisoned beings too clever to maintain our peace of mind. The undead god, which is the monstrous power of cosmic creativity, blindly spits up creatures that are instinctively opposed to living alone, only to create a second dead end for these social beings: when they huddle to escape the anguish of loneliness, the majority who are relatively docile place themselves in the clutches of oligarchs.