"Standard run" from the 1972 edition of "The Limits to Growth"
In 1972, "The Limits to Growth" presented a set of scenarios for the future of humankind, which mostly involved decline and collapse of the world's economy. These scenarios were the result of solving a set of coupled differential equations and, for most people, the reasons for the predicted behavior of the economy remained obscure and imperscrutable. As a result, the results of the study were neither understood nor believed.
As I argued in a previous post, we tend to understand the world in narrative terms. We think in words, not in equations. And we tend to use words to arrange concepts as if they were actors playing on a stage. In the end, it is not a less legitimate way of modeling the world than using equations. So, I found in the blog of John Michael Greer (the "Archdruid") an exceeding lucid and compact description of the reasons why civilizations tend to collapse. And here it is: no equations, no graphs, but it couldn't be clearer than this.
Excerpt from a post by John Michael Greer, from "The Archdruid Report"
The process that drives the collapse of civilizations has a surprisingly simple basis: the mismatch between the maintenance costs of capital and the resources that are available to meet those costs. Capital here is meant in the broadest sense of the word, and includes everything in which a civilization invests its wealth: buildings, roads, imperial expansion, urban infrastructure, information resources, trained personnel, or what have you. Capital of every kind has to be maintained, and as a civilization adds to its stock of capital, the costs of maintenance rise steadily, until the burden they place on the civilization’s available resources can’t be supported any longer.
The only way to resolve that conflict is to allow some of the capital to be converted to waste, so that its maintenance costs drop to zero and any useful resources locked up in the capital can be put to other uses. Human beings being what they are, the conversion of capital to waste generally isn’t carried out in a calm, rational manner; instead, kingdoms fall, cities get sacked, ruling elites are torn to pieces by howling mobs, and the like. If a civilization depends on renewable resources, each round of capital destruction is followed by a return to relative stability and the cycle begins all over again; the history of imperial China is a good example of how that works out in practice.
If a civilization depends on nonrenewable resources for essential functions, though, destroying some of its capital yields only a brief reprieve from the crisis of maintenance costs. Once the nonrenewable resource base tips over into depletion, there’s less and less available each year thereafter to meet the remaining maintenance costs, and the result is the stairstep pattern of decline and fall so familiar from history: each crisis leads to a round of capital destruction, which leads to renewed stability, which gives way to crisis as the resource base drops further. Here again, human beings being what they are, this process isn’t carried out in a calm, rational manner; the difference here is simply that kingdoms keep falling, cities keep getting sacked, ruling elites are slaughtered one after another in ever more inventive and colorful ways, until finally contraction has proceeded far enough that the remaining capital can be supported on the available stock of renewable resources.
See also "A theory of catabolic collapse" by J.M. Greer.