There are many reasons for the fall of the roman empire. One reason is government corruption, the size of Rome alone made it hard to control Rome. It also lost all of its tradition and value to the sudden growth in Christianity. Barbarian tribes were also a problem, because this was about the time the Huns became a threat to nearby countries. Rome was eventually overthrown by a German barbaric leader, meaning that Rome's rule had officially come to an end.
Hope this helps :) if you need to elaborate you can, there's plenty of room for describing each disaster.