Nice to see you again.
There are certainly no shortage of ideas about what sorts of things
led to the downfall of the Roman Empire -- one source below lists no
less than 210 contributing factors.
Gibbons' "Decline and Fall" certainly looms as the great masterwork on
this topic, but there are certainly other sources, and other pieces of
information that have emerged in the intervening years since Gibbons'
work first appeared.
I've included some of the best sources that I know of for your review,
and these are listed below.
From your question, I understood that you were mostly looking for
these types of sources. However, if I have misconstrued your question
at all -- or if you simply find that you would like any additional
information -- just post a Request for Clarification to let me know.
As always, the question is not answered until you say it is, so just
give the word if you need anything else.
All the best,
Reasons for the fall of the Roman Empire
All left Rome open to outside invaders
[the reasons discussed here include]:
Decline in Morals and Values
THE FINAL BLOWS
The Fall of Rome
Reasons for the decline of the Roman Empire.
Timeline of the end of the Republic
In popular history, the year 476 is generally accepted as the end of
the Western Roman Empire. In that year, Odoacer disposed of his puppet
Romulus Augustus (475-476), and for the first time did not bother to
induct a successor, choosing instead to rule as a representative of
the Eastern Emperor (although Julius Nepos, the emperor deposed by
Romulus Augustulus, continued to rule Illyricum until his death in
480, at which point Odoacer annexed the remainder of the Western
Empire to his Italian kingdom). The last Emperor who ruled from Rome,
however, had been Theodosius, who removed the seat of power to
Mediolanum (Milan). Edward Gibbon, in writing The History of the
Decline and Fall of the Roman Empire knew not to end his narrative at
476. The great corpse continued to twitch, into the 6th century.
Rome -- The Empire Declines
With Commodus (180?192) the decline of the empire is usually said to
have begun. The age of the Praetorians was then at hand, when the rise
and fall of emperors was determined by this elite corps of soldiers.
Septimius Severus (193?211) was unusually able for his period; he
campaigned with success against the Parthians and against the Picts of
N Britain. His son Caracalla is noteworthy for extending Roman
citizenship to all free men of the empire and for the famous baths
named after him
[This is an exhausitve and comprehensive site, with a lot of
information to consider. In particular, note the links here to the
major segments of the history of the Roman Empire]:
The High Point
[for instance, here's the link to the 'Collapse' site]:
[note as well the "Collapse Chronology" on the left side of the page.
210 Reasons for the decline of the Roman Empire
The Decline and Fall of Rome
Rise and Fall of the Roman Empire
[note the link at this site to the malaria connection]:
Malaria May Have Hastened the Fall of Rome
THE DECLINE AND FALL OF THE ROMAN EMPIRE
[at this BBC site, you can listen to the audio of a show on the
Decline and Fall of Rome. Just click on the following text]:
Listen to this edition of In Our Time
[very extensive presentation here, from an old but authoritative text]
Outlines of Roman History
by William C. Morey, Ph.D., D.C.L.
New York, Cincinnati, Chicago: American Book Company (1901)
THE DECLINE OF THE EMPIRE
23. Reign of Augustus
24. Julian Emperors
25. Flavian Emperors
26. Five Good Emperors
27. Decline of Empire
28. Reorganization of Empire
29. Extinction of Western Empire
Again, I hope you have everything here that you need, but if not, just
give me a holler.
search strategy: Google search on [ (decline OR fall OR collapse) "roman empire")