I was recently exposed to the notion that oligarchies are by nature destined to lead to population collapse. Without even completing the argument of the most recent book I was reading, the simple, elegant logic behind it became utterly clear.
There is a physical limit to how much physical stuff any of us can befit from using, or even put any judgment into using. When we consume more, the rest is largely wasted from our perspective, and from the perspective of others who might otherwise have had other uses (such as survival) for the raw materials and energy that went into making it.
Waste piles up with its attendant health hazards. If only a small number of people have enough power to consume most of what’s available, the people who don’t have enough quality stuff to survive and thrive compete for what’s left. This all results in increasing stress (along with attendant violence) and declining health among the majority of the population.
Processing raw materials into stuff to be consumed is almost by definition done by the majority. This is because no matter how efficient a small number of people may be (with any technology), more can be consumed if more people produce it. As the majority suffers, the quality and quantity of stuff goes down, which makes things even worse as part of a vicious feedback loop. Eventually, most people die.