Zenpundit has a great post on the question: Do Oligarchies Create Insurgencies? His best answer seems to lie in this bullet point:
Oligarchical policies seem to increase the likelihood of rebellion by being repressive, economically exploitative, politically unrepresentative and also incompetent, governing in opposition to the interests of a majority of the population.
One part of that bullet point sparks my interest: “governing in opposition to the interest of a majority of the population.” You see, while the military experts will disagree, I don’t think insurgencies are opposing forces against an incumbent force. Insurgencies are forces perpendicular to incumbent forces.
What this means is insurgencies push the incumbent force one way or another, much like the democratic and republic parties in the US, but there is no friction between them. Friction takes a normalizing force that, sort of, holds both forces in repulsion or attraction, but mostly acts as a regulating force.
In a totalitarian ruled country, there is friction, as all forces are opposing or attracting, while the normalizing forces are economic in nature. The normal force dictates that you live or die, because of your ability to use (or not use) resources, according to the commands of the totalitarian ruler. In physics this means that the economy acts as a force perpendicular to both the totalitarian ruler and those he rules.
The ethics of a society are also forces that produce friction.
Insurgencies do not appear everywhere and where they appear they do not all enjoy similar success. Some are crushed virtually before they begin; other take over the state only to face new insurgencies against their own brand of government.
It is the ethics of the head of government that crushes the insurgency and it is the ethics in the environment of those that take over the state that creates another insurgency. Only it is really not an insurgency until the forces in opposition are aligned perpendicularly. Until then, it is called a civil war.
Forces perpendicular to each other have no such normalizing (regulating) force; so they don’t support friction, but they do represent an insurgency together with an incumbent force.
Forces perpendicular to each other are both a part of the same economy, only push it one way or the other (as does an insurgency), according to logic that aligns the ethics in the relationships between they who have and they who have not.
This is why an oligarchies produces an insurgency more than a totalitarian lead country; an oligarchy needs a poor class to align perpendicular to itself within the economy, while a totalitarian lead country only need resources and the ability to command those resources.
Without the poor class there is no logic to an oligarchy; without resources, and the ethics to maintain those resources, there is no totalitarian form of government.
With an authoritarian form of leadership the logic changes, as the ethics are aligned to give authority to one class by the other.
Either way, there is not much room in an oligarchy, totalitarian, or authoritarian society for a middle class. The middle class is the unique element, between an incumbent and an insurgency, within a society.
The middle class represents that part of the society that are not close (to either the rich or poor) nor deeply divided (they are members of the same society of the rich and poor).
This not close, but not deep, positioning represents a square wave, whose relationship to the rich and poor of the society is neither perpendicular nor aligned in opposition. A middle class needs a different kind of logic than that which is found in an oligarchy, totalitarian or authoritarian form of governing. An insurgency will come, but only after the middle class is , for all its logic, destroyed. In physics or electrical engineering terms, the middle class needs the logic of the dwell in the impulse.
My guess is that a middle class will only survive in a democracy representing all the people, or a republic that is willing to regulate the oligarchy, totalitarian, and authoritarian elements of the logic of its representatives.