There remains the question, What is the precise economic statement of the final collapse? It is easy to figure that in terms of _(a)_ increasing barbarian enterprise, stimulated by the personal experience of the many barbarians who served the Empire, and of _(b)_ increasing moral weakness on the part of the whole administrative system. And doubtless this change in the balance of military energy was decisive. When utter weaklings sat by heredity in the imperial chair, at best contemptuously tolerated by their alien officers, the end was necessarily near. The most incurable disease of empire was just empire; ages of parasitism had made the Roman ruling class incapable of energetic action; and the autocracy had long withheld from citizens the use of arms. But the long subsistence of the Eastern Empire as contrasted with the Western proves that not only had the barbarians an easier task against Italy in terms of its easiness of invasion, but the defence was there relatively weaker in terms of lack of resources. This lack has been wholly or partly explained by quite a number of writers[218] as a result of a failure in the whole supply of the precious metals--a proposition which may be understood of either a falling-off in the yield of the mines or a general withdrawal of bullion from the Empire. It is difficult to see how either explanation can stand. There was already an immense amount of bullion in the Empire, and a general withdrawal could take place only by way of export to the barbarian east in return for commodities.[219] But the eastern provinces of the Empire were still in themselves abundantly productive, and after the fall of Rome they continued to exhibit industrial solvency. No doubt the plunder of Rome by Alaric (409-10) greatly crippled the west, and the loss of Gaul and Spain was worse; but while the Empire retained Africa it had a source of real revenue. The beginning of the end, or rather the virtual end, came with the conquest of the African province by the Vandals (430-40). In 455 came the sack of Rome by the Vandals, whereafter there remains only a shadow of the Roman Empire, till Odoaker, dismissing Augustulus, makes himself king of Italy.