>>17948647 (OP)
>What were the reasons the Germanic peoples were able to defeat the Romans?
standard process of imperial decline. to be honest, it's arguable romans didn't even really exist in the late imperial period. rome was an immense megapolis populated mostly by slaves, freedmen, a handful of aristocratic families who owned everything (and everyone) and a minority of plebeians who lived off of handouts and were not allowed to serve any function in the life of the state.
both politically and demographically, rome ceased to function as a city. predictably, the capital was moved to a totally different place - rome the city no longer had any unique character that necessitated its centrality.
> And why is it that, since the fall of Rome, Mediterranean peoples have not been able to match the technological level and development of Northern Europe?
this is total bunk, meds (specifically italians) were both richer and more cultivated than the average northern european until quite late, well into the enlightenment period. moreover, "northern europe" is a very poorly chosen term. scandinavia was a dumpster. i think what you are thinking of is the britain-france-germany region and its technological and economic development.