Answer:
Wide-spread political corruption led to a weakened military, which allowed Northern invaders to come in and seize control.
Step-by-step explanation:
There are various reasons that caused the Roman Empire to fall, and the capital moved to Byzantium. However, top of the list in the underlying cause for Rome to fall, and empire to move to Byzantium is "Wide-spread political corruption led to a weakened military, which allowed Northern invaders to come in and seize control."
This was evident during the second and third centuries, in which there was so many civil wars and political power tussle, that led to over 20 Emperors to reign in just about 75 years. This was coupled with the widespread corruption of the Roman Senate.
During this period, many Roman citizens avoid to join the military. Also the Northern Invaders often referred to as Germanic barbarians were constantly invading the Roman Empire. Eventually, Constantine decided to move the Empire to Byzantium in Constantinople.