The Roman Empire fell for many reasons. I think that the two biggest reasons were that all of their leaders were being assassinated by their own people, so there were no laws that were carried out. The second reason I think is because when the Huns started taking over Rome some romans were happy they weren't being ruled by roman laws. Romans said that the government was falling apart and ruining their state.
In a chart of the ways roman emperors died 13/22 emperors were assassinated by their own people and were 22 leaders from 235-285 CE. Emperor's only ruled for a short period of time so no laws were put into action and there was never a set plan for the development of the Roman empire. The many assassinations also taught