It was not the complexity per se, but the cost of that complexity that came to be unsustainable. When wealth yeilded by the conquered provinces no longer exceeded the cost of conquest the situation began to change. This was a centuries long process. And with the end of expansion came the end of plentiful slaves. That was a major energy input to the empire. When those slaves died of old age, the plague or overwork they could not readily be replaced. But there was a time lag involved and the market for slaves did not disappear but did become more expensive.

But meanwhile the costs of of the systems that had to be supported rose but income did not. The empire still had to be defended, but that defense no longer generated a surplus. Rome still needed grain to feed the urban masses. Roads and aqueducts still needed to be maintained.

To me the argument is reasonably clear. The Western Roman Empire ran largely on slave labor. That slave labor was cheap when the Empire was expanding but got progressively more expensive and scarce after the time of Augustus. The military, the civil engineering and the administrative apparatus had all been developed when slave labor was cheap and abundant. They became more difficult to support as slave labor became expensive and less abundant, but the needs did not change. This was especially problematic during emergencies, such as barbarian invasions, when large amounts of money were needed. In order to meet these challenges, the Empire essentially turned to cannibalism and began consuming its base in a downward spiral that led to collapse.

To say that the problem was that the emperors made bad political decisions is a facile non-answer. The basic pattern of Roman society had been set during the middle of the Republic when the conquests began. Policies such as not taxing provinces in the Italian Peninsula may have been unwise in the long term, but they were eminently practical politically at the time and by the time the problems struck home such practices were traditions dating back hundreds of years, longer than the USA has existed. Likewise with slave based agriculture, domestic service and handicrafts.

The emperor required some acceptance from those he ruled. To overturn traditions and privileges dating back a hundred years or more into the Republic and imposing taxes on people unused to taxes, imposing taxes on the most powerful men in an historically oligarchic society, overturning the social basis of the society by uprooting its slave basis, etc. was simply a non-starter. A thousand years later the Norman Kings of England and the Kings of France, Spain and Portugal, with varying degrees of success, began the process of breaking down the power of the nobles, a process that took the better part of another millennium.

But perhaps I am misreading your comment. What better political decisions would you suggest that they have made and how do you suggest they could have carried them out?

To me the analogy between the problems of the emperors with the aristocracy and the problems we currently have with the financial sector seems familiar. As does the problems with a massive increase in the cost of the energy source on which our civilizations have been built. But I believe we have a better chance of changing those aspects of our society than did the Romans. Our population is vastly better educated and the existing system is less well entrenched, not explicitly included in the Constitution and of more recent origin than was the case with Rome. And while no energy source now available offers the EROI of $2/bl. oil, which provided ratios of over 50/1, ratios of 20/1 are available, if we can embrace them. And better resources may still emerge.

Or our current elites can continue on their pigheaded path, devouring the basis of the US economy for their short term profit, until everything collapses and then they may prevent the emergence of anything better. But I believe we are less doomed than was Rome, but perhaps not by so much as we would wish.

 

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."

In general, arguments based on energy returns, technological advancements, and ecological limits are interesting in the close attention they pay to factors overlooked.  However, to the degree that they take attention away from what were (in my opinon, at any rate) purely political decisions, or the outcomes of fights between political and economic elites, they are a serious distraction.  In a way, they seem part and parcel of the same project that underlies much of economics, to remove a large part of human life from the realm of agency and choice, and reify it as a force of nature.

I agree that any approach can be used to distract from rather than illuminate a problem. But the political decisions, IMO, have to be viewed in the terms of How Institutions Think, as described by Mary Douglas. I have written on this subject in comments that TGB turned into a diary: Malleable social reality. One of the comments in that diary has a portion of Douglas' argument quoted. Christianity was an available option as a state religion in the time of Constantine, so he could make it and official religion by decree.  An effective alternate understanding and organization of Roman society in the Western Empire was not similarly available to my knowledge. That is a major reason to push alternative organizations of contemporary societies and economies into the public sphere today - so they are familiar and available to be considered in case the opportunity arises.

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."