(Originally posted at The American Catholic. I thought the history mavens of Almost Chosen People might find it amusing.)
You know, I am old enough to recall when NASA was all about space exploration. Under the current administration it appears that NASA is mostly concerned with supporting the agendas of the Obama Administration. Case in point, a NASA funded study of epic historical illiteracy:
Go here to read the rest. What this nonsense on stilts actually reminds me of is the way conservatives in the sixties would point to current sexual immorality and state that is how the Roman Empire fell. Please. The three main factors in the fall of most civilizations are: catastrophic military defeat, the growth of governmental bureaucracy that stifles initiative and imposes crushing costs on the private sector and increasingly sclerotic elites who simply are unable to meet new challenges. I almost feel like sending the authors of this travesty my 12 volume set of Toynbee’s A Study of History which has several thousand pages devoted to why societies collapse, but I doubt if they would read it. (Toynbee had a lot of crackpot ideas, but the hundreds of historical vignettes that dot his Study are invaluable.) You can go here to read the paper. It is the usual type of trash produced these days in too much social “science” where math substitutes for actual historical knowledge. The study reaches its preferred conclusions, ecological catastrophe and “inequality”, by loading up the study with societies like “Great Zimbabwe”, where the historical record is non-existent to very poor, and ignoring the collapse of societies where the historical record is quite good: Rome, Ancient Egypt, various Chinese dynasties, etc. Almost all the works cited at the end of the study are recent, in the last decade or so, and most devoted to precisely the same ecological interpretation of historical events favored by this study. Garbage in, garbage out in other words. Politicized junk history is worthless and this study is a prime example. Stick to space exploration and Tang NASA, History is most definitely not your strong suit.
Donald R. McClarey
Paul Zummo
Almost Chosen People 
The Roman Empire was killed by four things: taxation, centralization, the lack of a law of succession to the throne, and terrible frontiers. Taxation was necessary to keep up the enormous military establishment that kept the empire alive, but it became both more onerous and more unfair as the senatorial classes in effect wrote themselves out of the taxation rolls and left the lower classes to face the music. Centralization meant that nobody except the emperor could really fight a war, whether in Britain or in Iran, and that every commander who did so without being an Emperor was automatically suspect. The lack of a proper law of succession to the throne made usurpation and civil war chronic. And the borders that cut Europe in half across, leaving much of the best arable land to the barbarians, and exposed the best part of the Empire to Persian assault, meant constant over-expenditure on defence… vicious circle.
The Roman Empire effectively ceased to exist with the murder of the emperor Constant II in 688 AD; not only because that led to a terrible crisis in which Constantinople itself was besieged, but because what arose from the ashes was a wholly different system. Constant had actually taken a bold initiative, moving the capital from Constantinople to Syracuse, in order to take action against the Arabs in North Africa – which was still mostly unconquered and could have been rallied against the Arabs. In effect, Constant was trying to revitalise and consolidate the old cross-Mediterranean axis that had been the heart of the empire. But the first thing he did when he took over in Byzantine Italy was to raise taxes – and kaboom. A dagger took care of that. A couple of years later, Carthage fell, and within a generation the Arabs had taken Spain and Sicily and were under the walls of Constantinople.
“The Roman Empire was killed by four things: taxation, centralization, the lack of a law of succession to the throne, and terrible frontiers.”
Agreed, along with an inability to raise troops from civilized regions. Marius and Caesar produced magnificent troops from the slum dwellers of the Subura but this became a lost art under the empire with the military manpower increasingly being drawn from frontier regions.
I don’t quite agree. Many of the legions were in fact recruited in places such as Syria, which were at the time the heartland of the empire. Josephus, IIRC, says that the legions that destroyed the Jewish rebellion under Nero and Vespasian identified with the Syrians and had picked up their quarrel with their Jewish neighbours. At some point around the turn of the fifth century, however, the system broke down, and the empire ceased to recruit individuals – in which a considerable amount of barbarians had always been present, since service was well paid and allowed veterans to become Roman citizens – but rather to make political treaties with barbiarian kings who effectively placed their tribes at Rome’s disposal. I suspect a kind of military Gresham’s Law: it turned out to be – in the short term – easier to bring in a whole tribal unit already trained and ready to fight than to go through the expensive and long process of training legionaires. Much of the so-callled barbarian invasions actually amounted to negotiations between the empire and barbarian treaty partners as to how much land the latter could claim for their task of manning the imperial frontiers. Of course, in the end what happened was that political power migrated to the hands that held the swords.
It depends upon what period of the empire we are talking about Fabio. For example consider the Emperor Aurelian and the other soldier emperors of the late third and early fourth centuries who were from the Balkans. This may have been due to the simple fact that the Legions recruited where they were stationed and most of the legions, most of the time, were stationed in frontier areas. The fact that over time the military profession became very much of a family affair with sons succeeding fathers in units would add to the recruitment from areas where ex-legionnaires retired, which tended to be around where their units were stationed. Your argument about a military Gresham’s Law is a good one, especially with more and more of the Empire bureaucracy lacking any military experience themselves and not recognizing the drawbacks of mercenaries. Vegetius and his Epitoma rei militaris demonstrates how little actual military experience most late Roman civil servants had, with his longing for the Army of the Early Empire without any real understanding of why the Roman military had changed over the centuries.