“declining moral values and political civility at home, an over-confident and over-extended military in foreign lands and fiscal irresponsibility by the central government”.
Where to start? As far as "declining moral values" goes, I can't see that the Western empire was any more decadent in the 5th Century AD than it was in the 1st Century BC. Heck, by the early 400s, gladiatorial combat had been outlawed after declining in popularity for half a century, monasticism was increasing in popularity, and Christianity of an early and austere form was the state religion. This tends to come as a surprise to people who hear "Rome" and immediately think of that bootleg copy of Caligula they watched on their parents' Betamax back in the day. As far as "political incivility" goes, "politics" as we know them were largely unknown in the late empire; the Senate had devolved into a senescent gentleman's club, and the imperial administration was thoroughly autocratic. Rome's military was overstretched, but it was overstretched within its own frontier and not in foreign lands. The manpower shortage in the legions became acute, with citizens of the empire going so far as to cut off their own right thumbs to avoid conscription. Recruits had to be branded to reduce desertion. The desperate gambit of forcing the sons of the men who served in the limitanei, or border militias, to be literally born into the garrison didn't even help. Which brings us back around to foederati.
The Roman army was stretched too thin to prevent constant incursions by Germans, most of whom were less interested in plunder than they were in settling down in Roman territory and enjoying the good life, which they didn't understand came with things like property deeds and taxes attached. Thus came the foederati system. Tribes would be allowed to cross the border and live under their own laws, speaking their own language, in their own areas within the empire, on the condition that they signed a treaty of friendship with Rome and that they provided troops for the army. These troops used their own equipment, fought in their own style and under their own leaders, and by the time of Stilicho or Aetius, it could be hard to tell a Roman army from the Germans or Huns they faced.
In the end, the Roman empire in the west never really fell. It just sort of dissolved, with tribal areas growing like inkblots, and tribes moving into the empire without asking permission. When all was said and done, they just sent the crown back to Constantinople, as there wasn't really an empire in the west any more, only a bunch of Germanic kingdoms with Roman priests and merchants and clerks. So, yes, the end of the empire in the west is fascinating history. I just wonder how much of it Mr. Walker has studied.
(H/T to Cameron Bailey.)