Why Rome Fell - 210 reasons

[Flavivs Aetivs]

For instance, how could "excessive urbanisation" have contributed to the fall?

Well, if too many people migrate to the city, like happened in Rome, for the free food, no taxes, etc., there are too few to work the farms and manage production. For a welfare state (bread and circuses free) to work, there must be increased import of goods, services, and supplies to feed the increased numbers of recipients. Without that, the urban area becomes filled with discontented population, which endangers the city itself. The seeds are well watered for a civil revolt. Harbinger if ever I saw one.

That was a major cause - the loss of Africa meant the Romans could no longer support their welfare state. Aetius cut taxes on some landowners, put taxes on the Rich (something they had been avoiding because the Italian landowning class controlled the senate, but the gallic landowning class still paid taxes) and a number of other laws in order to fund his army. He also got rid of the burdenous tarriffs on foreign merchants and some of these measures re-vitalized the farming industry in southern Italy. The west was still horribly in debt and still needed massive cuts though.