The decline of the Roman Empire was brought about by a number of reasons. The three primary reasons that caused the Roman Empire to fall were political, economic and military in nature. From the 4th to 5th century AD, the people at the helm of power in Rome were finding it increasingly difficult to defend the Roman Empire against invasions. Many Romans were displeased with the authoritarian leadership in Rome, and the empire started to experience internal strife. The military might of the Romans, which the empire was famous for, also started to diminish as it became more difficult for Rome to produce the quality of soldiers that it had in the past. Furthermore, with the drying up of the funds from other cities, the economy too began to crumble.
Monetary taxation, which was the earlier system of collecting revenue from the people, was substituted by direct requisitioning. In this system, the Roman Empire took food grains from the farmers, cattle from the herdsmen, and iron tools from the blacksmiths. The workers were also compelled to work in the same occupation.
Therefore, if a particular occupation or business was not going well, the people associated with it would be impoverished. This led to unemployment on a large scale. As a result, resentment among the Roman people began to grow. Additionally, the excessive intake of alcohol by several disgruntled people of Rome resulted in poor overall public health. The contaminated water that came through lead pipes further deteriorated the health of the Roman people.Via http://www.thefreeresource.com/the-roman-empire-timeline-of-fun-facts-and-resources-about-its-rise-and-fall