Joseph Tainter has an interesting essay titled Complexity, Problem Solving and Sustainable Societies. His thesis is that humankind, in order to solve practical problems, increases the complexity of the systems that go toward a solution. Over time this complexity needs to be subsidised by increasing energy - lest they collapse.
Tainter includes a discussion of Rome in his thesis. As Theophile Escargot argues, Rome hung around for so long that you can fit any model into its collapse:
[T]he Decline of Rome is a useful ground for arguing absolutely anything. Want to build up defence spending? Argue the Roman empire fell because it didn't secure its borders against the barbarians. Don't like immigration? Argue that their mistake was letting Visigoth asylum-seekers settle inside the Danube border after fleeing the Huns. Like free trade? Argue like Pirenne that the Arab restriction of trade routes did for it. Don't like religion? Follow Gibbon and say it was weak-minded Christianity that softened it up.Tainter's argument is that complexity, and ability to problem solve with increasing complexity is a restraint on a society and economic system. The only way it can be overcome is with external energy inputs. Humans generally choose a simpler and easier method where they can, but often, there is no choice but to become more complex and usually through greater "differentiation, specialisation and integration". Tainter describes complexity as an economic process as it "levies costs and yields benefits" and as such is an investment that has a quantifiable return. Humankind has generally chosen the cheapest, easiest and least complex solution first. But once that is exhausted increasingly complex solutions are found with diminishing returns. A good example is oil extraction. Most of the easy oil deposits have been found, so now we drill offshore and are even contemplating using the oil shale in Canada for energy.
The empire came to sustain itself by consuming its capital resources; producing lands and peasant population. The Roman Empire provides history's best-documented example of how increasing complexity to resolve problems leads to higher costs, diminishing returns, alienation of a support population, economic weakness, and collapse. In the end it could no longer afford to solve the problems of its own existence.Interestingly he discusses industrialisation, which was the rise of the British Empire, though Tainter does not mention it that way. The overpopulation and denuding of forests for energy led to the use of coal. The easy deposits were mined, so deeper and deeper shafts were driven but that led to ground water issues. Which was solved with steam powered pumps. He writes:
What set industrialism apart from all of the previous history of our species was its reliance on abundant, concentrated, high-quality energy. With subsidies of inexpensive fossil fuels, for a long time many consequences of industrialism effectively did not matter. Industrial societies could afford them. When energy costs are met easily and painlessly, benefit/cost ratio to social investments can be substantially ignored (as it has been in contemporary industrial agriculture). Fossil fuels made industrialism, and all that flowed from it (such as science, transportation, medicine, employment, consumerism, high-technology war, and contemporary political organization), a system of problem solving that was sustainable for several generations.So energy subsidises complexity, to the point that complexity's true cost and diminishing return on investment can be hidden. Such that Tainter writes that for our ability to solve problems with greater complexity, "the availability of energy per capita will be a constraining factor".
