There are valid reasons that can justify the event. Some of these causes can be the invasion of Germanic rulers and the barbarians. Secondly the economic conditions of the empire and thirdly the religion Christianity. If the answer is supposed to be a single reason, one can take it as the result of poor leadership.
Dissemination of the currency in the Western Empire was one of the chief reasons that led to the annihilation of the financial system. Moreover, the Treasury was burgled by the barbarians that serving to choke the development the Empire. The Roman Empire consisted of a rotten infrastructure. During the years, the buildings were damaged and the famous Nero’s Fire devastated the whole state. Left with a few regions, the major parts of the empire expired while some of them distorted due to the side-effects of smoke. Since the currency was deficient in distribution and pilfered by the barbarians, the government lacked funds to renovate the degenerating structures (Gibbons and Womersley).