One of the things that really hammered me in my reading (over one week) of both Ward-Perkins and Peter Heather's books, is what a disaster, economically speaking, the loss of Africa was in the 430's, when the Vandals, having traveled to North Africa from Spain, took such cities as Carthage.

I had not understood that, in the last several decades as northern Europe was increasingly fraught with constant incursions, how disrupted the economy, trade, AND most importantly, crops had become. Africa had for several generations taken over and had become Rome's breadbasket - peaceful, immune to invasion (it seemed), becoming wealthier and wealthier by trade.

It is my strong impression that when the Vandals finally crushed the Roman culture in North Africa, war, the collapse of trade, and other disasters reduced the ability of the northern Mediterranean nations to use North Africa's produce. Over a few decades, this dearth became a true death-knell for the economy in Rome, as thousands of tax-paying North African Romans were displaced by barbarians who paid no taxes and produced nothing for Rome.