- excessive outsourcing of the army to germanic foederati. One should never outsourcing the core of its defence. The ERE, on the contrary, saw the danger and led a "de-germanization" of its army
It's essentially an a posteriori threat : because Romano-Germans armies eventually get power, we assume that it was the problem.
But it's probably much more a consequence of political troubles in Rome, than their cause : up to the middle of Vth century, use of foederati (that should be distinguished from Barbarian presence in Roman army, that had a long history and was clearly smoother) wasn't automatically synonymous of loss of power; and eventually was necessary giving the constant lack of manpower Romania knew after the great epidemics.
It's really less use of foederati (that was about integrating whole polities in Romania, instead of wasting already limited ressources fighting them all, IIIrd century way) than a general decline by the Vth century (and even there, it's essentially about opportunism : for exemple Franks, while foederati, weren't really that of a threat. But Visigoths were, and the integration of Hispano-Roman or Gallo-Roman nobility may not be totally unrelated)
since it no longer had the vast resources of the east, the WRE was more or less forced to opt for a much more decentralized organization. The western emperor had become obsolete and unfit to the new situation. This was a very long-run trend that basically lasted for 6 centuries. The WRE split into smaller kingdoms and then these kingdoms split into smaller principalities. This was the age of feudality.
There, I'd disagree entierly. Feudality conceptually doesn't appear before late Carolingian times. The whole principle of systematical devolution of power associated with property is unknown in Merovingian Gaul, or Visigothic Spain.
Rather than a long-trend of decentralisation, we rather have more a continuity of Late Imperial structures (up to the alleged germanic co-kingship of Franks or Goths, and that is probably issued from Late imperial origins), adapted to a post-imperial situation but essentially the same than before WRE collapse.
Not that you didn't have a decentralisation of power, but it already existed during the Principate : if something, the relative increase of bureaucracy allowed a more direct interventionism from the emperor.
And not that the west was cut of from trade roads : these really suffered at the Vth century, that's no question (consequences were felt up to Scandinavia), but recovered more quickly that you make it (
Dark Age Economics is a must-read) with not only their revival and growingly more important goods but with the appearance of new trade roads (in North Sea, notably).
It was more or less short-lived in Mediterranean Sea, granted, but it's due to the Romano-Persian wars (and decline of important trades or exchanges, such as gold) and first Arab conquests only parachieved this even before they reached Africa.
Rome beat equal Empires: Carthage, the Seleucids, Macedonia
Not equal empires, on several (while admittedly different) grounds.
Carthage was powerful, but lacked deep commitment to military structures that were more or less looking like what existed in the Late Republican era : reign of ambitious, demagogic generals. Eventually, such division didn't really helped.
As for Macedonia or Seleucids, we're talking of quite declining empires, more or less falling apart from assaults on the East or "balkanisation" in Anatolia or Greece. Not little wood, granted, but Rome made quite opportunistic attacks.
Under the Princapte, Rome barely managed to defend against Parthia
Giving that Parthians were never a structural, and vital threat to Romans, I think you're unfair there.
Of course, Late Republican armies were harshly beaten, but we're in the case I mentioned above. Not much commitment to one front, reign of the ambitious and lack of real unified strategy. Eventually Caesar won because he dealed with Gallic city-states and tribal states, not an unified, ressourceful, wealthy and strong empire.
It would be like wondering at someone being able to beat the crap out of a random guy in the street, while considering that his pal not being able to do so against a professional catcher means he sucks; if you pardon me the analogy.
and not even brought off to annihilate the Germanic tribes unter Arminius
USA weren't able to annihilate Viet-Cong and Viet-Nimh, that weren't remotely able to being a world power as America. Does that means that USA are going to collapse because it's no longer crushing natives efficiently?
And the accomplishments of Byzantium are... more or less miserable.
You mean...living on for
one millenia, being able to repeal Arab conquests and falling only due to being attacked from every side at once?
You must have pretty much high standards.
In fact, in general terms, Rome was founded unter a king, grew under a republic, gained from the expansion under the Empire and lost its conquest (with some selective restaurations and reconquests, I know).
You're giving, IMO, too much credit to historiographical definitions : for a Roman of the Ist century, there was no difference between Principate and Late Republic...Because there were not much difference, safe that Augustus posed as an arbitle instead of still ongoing civil wars.
The same way, early Republican Rome (at least up to the IIIrd century) was barely distinguishable (even institutionaly) from Royal Rome. What provoked the changes were conquest and redistribution themselves rather than the contrary : by Augustus, you had the feeling that more territory would be too much (not unlike why Chinese dynasties never went into Borg-like conquest).
Some fine tuning was still considered useful, but it's more about fear to over-stretch, rather than being due to a structural decline.
But most importantly, the competition within the ruling class was reduced to a strict minimum, since the power of the Senate and his magistrates was abolished, and thus, the main reason for conquest ceased to exist.
There as well, I think you're giving too much credit to emperors : at least during the Julio-Claudian dynasty, you had repeted attempts to make the Senate a political partner, that failed because of the unability to totally complete monarchism (not in the sense of kingship, but on the antiquity meaning, as in popular strongmanship) with a more aristocratic institution.
If something, the loss of Senatorial power should be put as military-driven emperors as Vespasians or Antonines; with the imperial power being more and more dependent of military abilities and role.
and meanwhile, the Germanic and Persian enemies grew in strength.
The unability to Persians (and even more Germans) to pose an existential threat before the...what Vth century would point otherwise. While Romans were able to ravage the hell out of Mesopotamia (a critically strategic region for Persians) regularily, Parthians never went even remotly close to do the same on Roman core regions.
As for Germans, as disruptive the IIIrd century raids were (and it's not due to a military problem only, rather the consequences of deadly epidemics happening in the same time), they never really went the way of destroying the imperium (admittedly, de facto dividing it up).
If something, they grew more and more integrated to Rome, rather than forging empire (You can safely date most of Vth Germanic peoples ethnogenesis from this period).
The stagnation became decline, and the decline mutated into downfall.
I don't think that a decline going on for five centuries can be called a decline at all. It's simply handwaving too much immediate factors that happened in the same time than the political collapse (already mentioned above), and eventually doesn't explain anything historically because not being directly tied to the historical conditions of this collapse.
