Late Roman Army during the 5th century

[starman2012]

Aetius did not have to rely on hunnic mercenaries - he merely had an edge with them.

But the Huns were the decisive element in the campaigns of the 430s, against Burgundians and others. If Aetius had no "edge" without them, and evidently, could accomplish little or nothing without them, he definitely relied on them.

The Roman Army in the 430s (this is speculative and theoretical though) mainly consisted of The Old Gallic Field Army...

Speculative and theoretical indeed. What was the matter with those guys--unable to control, let alone eject, barbarians on Roman territory.

The Barbarians were not a problem - only chieftans had armor and the raids accross the borders were still mostly petty until the Goths came down the black sea.

Seaborne gothic raids occurred in the mid third century and were devastating; the biggest battle of the century was fought and won against them in 268. Even after that the gothic menace, and others never went away.

The army's increase was in the East, read Peter Heather's Fall of the ROman Empire and his EMpires and Barbarians, he's the one who proposed the increase in the size of the army to counter the sassanids who were a power ont he same scale as Rome.

It seemed that way around midcentury but not when Diocletian built his defenses. After Edessa, Persia lapsed into weakness. Carus's march to Ctesiphon seemed as easy as Trajan's. Narses was tougher but was no sapor and was beaten. The Strata Diocletiana represented a new approach to eastern security--more preclusive as Ferrill would've put it--but I don't know if it involved significantly greater numbers of men. As the events of c 257-268 showed, the Rhine/Danubian fronts were second to none as potential threats, so I don't think the new, theoretically bigger army was built to counter Persia specifically.

The Parthians were never a strong nation and Rome rarely had to deal with them on such a large scale.

Even long after Carrhae, the Parthians could be very dangerous. The Romans obviously took their threat seriously. Look what happened to Severianus c 161. And while the Sassanids were very formidable from c 252-60, their power also seemed to fluctuate e.g. wane at times. Already in the 260s Odenathus was able to advance deep into their turf with little if any resistance we know about. By 283-284 the Romans (including Diocletian) could've reasonably concluded the worst of the sassanid problem was behind them; it had died with sapor.

The army was the focus of Rome's economy and the required increse to counter the centralized army of the Sassanids meant inflation, and other factors which led to Economic Collapse.

The worst inflation was prior to Diocletian. As Heather notes, there is evidence for robust economic activity even in the late Empire. Provided a region was still under Roman control, it could provide a lot in tax revenue well into the fifth century.

The Rapid transition of emperors somewhat played into it, yes, but many of them were strong Military leaders.

True, I don't believe power struggles were the key issue.