I've read a lot about Punic Italy and the Marian reforms. It always seemed to me that Rome managed to muster armies numbering in the tens of thousands just from the peninsula and were fairly protected in the north by the Alps.
Given the above, even if the later Western Roman Empire was surrounded by "barbarians", could they not hold on to Italy at least, given that's where the martial civilization began?
I hypothesize some political, logistical, or economic problems, but could anyone explain it more in depth?
Given the above, even if the later Western Roman Empire was surrounded by "barbarians", could they not hold on to Italy at least, given that's where the martial civilization began?
This is a very broad and complicated question; I suggest you take a look at some of the frequently asked questions, here, relating to the "fall" of Rome.
Something to keep in mind while you browse is the concept of "late antiquity," the transitional period between the height of the Roman Empire ("classical antiquity") and the beginning of the "middle ages." Modern historians view late antiquity as a period of both continuity and change, such that the fall of Rome is more of a process than a signal moment like (say) the end of World War II. I hope this helps!