As shown in the diagram above, the moving of the Capital of the Empire to the Greek East had a devastating impact on the Latin West, effectively abandoning the whole West to repeated invasions, pillaging, looting, and a complete economic disruption. This left the West in a shambles, with death by warfare, anarchy, vandalism, starvation, and plague running rampant everywhere.
To quote the historian C.P.S. Clarke,
"Alaric and his Goths sacked Rome in 410. In the 5th century Visigoths settled in southern Gaul and Spain; Franks in northern Gaul and the Rhine; Burgundians and OstroGoths east of the Rhine and on the Danube; OstroGoths and then Lombards in North Italy, and Jutes and Saxons in Briain. Attila with a host of Huns invated Italy in 451. The [Western] Empire did not fall in a moment. Its policy was to recognise the conquerors and, as far as possible, absorb their rulers into itself as subordinate kings. ...There was in fact a good eal of 'gradualness' about the breakup of the empire. But in 476 the last Western Emperor, Augustulus, was forced to abdicate and the West was left without any emperor, except for the distant potentate in Constantinople, and kingdoms, independent in name as well as fact, were set up.
The Effect of the Invasions: - The effect has been variously estimated. AN earlier generation of scholars was inclined to lay stress on the masculine vigour of the barbarian as a fair compensation for the loss of civilization and culture. - The latest writer to deal with the subject, Boissonarde, can see nothing but evil in the invasions, and thus sums up their results:
"The idleness, stupidity, coarseness, ignorance, credulity and cruelty of the barbarians took the place of the well-regulated activity, polish, culture, relative humanity of the Romans. Far from regenerating the world, they nearly wiped out civilization altogether. Far from assisting its economic development, they ruined all activity by committing everywhere pillage, disorder, destruction. They created nothing, but they destroyed much and they put a stop to all progress for several centuries. The barbarian settlements produced one of the greatest retrogressions which the world has ever seen."This view is borne out by Gregory, Bishop of Tours (c. 573-594) whose History of the Franks is the principal source of our knowledge of the barbarians.
The breakdown of order and constant invasions of predatory bands produced an almost chronic state of famine. After a raid over Bourges we read: "There remained not a house, not a vineyard, not a tree; all was cut down and ruined. They even carried off the sacred vessels from the churches and burned the churches themselves with fire". Again, "Many a region did he lay waste again and again." In 536 A.D. ,50,000 peasants are said to have died of famine in a single province of Italy. Gregory alludes to famines as of common occurence. OF the year 580 he wrote: "IN this year almost all Gaul was oppressed by famine. Multitudes were reduced to making a kind of bread by drying and pounding grapeseeds or hazelblossom, and adding a little flour, while others did the same with fern-roots." Famine and the destruction of baths and sanitation were naturally followed by disease and plague. Boissonarde reports that in Britain in the 7th century, half the population perished during one visitation. Gregory writes as if dysentery and bubonic plague were endemic. In Auvergne, in 571, one sunday 300 people died in a single church. In Rome, Gregory saw 80 people dying in the street during a single Rogation procession. "
(Clarke, Short History of the Christian Church 1948),p. 104-106
The West was quickly lost to barbarian hordes and gangs, and the Roman Empire was obliterated in just about every province. A few maps illustrate the extent of the devastation.