I agree with the currency issue as a contributor, but still hold the barbarian invasion(s) were the largest nail. In Amorica, Gaul, and along the Danube, the Legions actually paid off the hordes and in a lot of cases, incorporated them in the army. In many cases they were brought in as officers. Thus, the dilution of the services led, in my opinion, to the Legion’s inability to defend the empire.
In he late 200’s, Diocletian(off all people) instituted a number of reforms that may have prolonged the Empire, but with continued invasions from Goths, Vandals, and the like, even his economic reforms couldn’t stop the decline.
No nation can survive under constant barbarian invasion, just look at the UK and Sweden..
The 2nd century empire was strong enough to defeat invasions.
Its not that the 5th century was much worse for invasions, it was that the Roman empire was much weaker and unable to resist the invasions.
Rome had many dozens of civil wars to help weaken and destroy them selves.
The Easter Empire lasted almost a 1000 years longer.
Who knows maybe that will be our fate.
Successful barbarian invasions are a symptom, not a cause.
If Rome was strong, the Empire would still be in existence in its initial form.
Even Caracalla’s Edict was a symptom of monetary collapse.
Look beyond the superficial.
The first rule everyone should learn immediately after high school: money rules; everything else is blah blah blah.
A nasty career in Big Pharma taught me that rule, and eight years of university studies only reinforced it.