There are any number of interpretations by historians for the efficient cause of the collapse of the Western Roman Empire; however the best answer is that there were a number of factors at work:
- The sheer size of the Empire (from the Atlantic to the Danube River) had made it difficult and expensive to both administer and defend. Although the Emperor Diocletian attempted to resolve this by dividing the Empire into more governable segments, this did not solve its more immediate problems. The Roman government was forced to employ Germanic tribes as mercenaries. Their loyalty was suspect at best, and ultimately they turned against the Empire.
- The pressure of Germanic Tribes forced into the Empire by the approaching Huns from central Eurasia was also a factor. In 376, one hundred years before the abdication of the last Roman Emperor, the Roman army agreed to allow the Goths to cross the Danube into the Empire. Poor treatment of the Goths caused a revolt. In the ensuing Battle of Adrianople, the Emperor Valens was killed. Once in the Empire, the Goths continued to wreak havoc.
- Internal disruption within the Empire. Since Roman armies were ultimately loyal to their commander, not the Emperor, several commanders were proclaimed "Caesar" by their armies. The end result was a series of civil wars, which ended when one general, Orestes, placed his teenage son on the throne as Romulus II Augustulus. The boy was feeble minded and merely a figurehead. Primarily as an act of exasperation, the Gothic general Odoacher, who had fought with the Romans, deposed Romulus and had his father executed. He then had the royal scepter and robe sent to l with a message to the Eastern Emperor that he was now the sole Roman Emperor.
An excellen discussion of the role of the Huns in the Empire's Collapse can be read in Christopher Kelly's The End of Empire: Attila the Hun and the Fall of Rome.