Answer:
The violent attacks from the tribes and the empires move toward Christianity, are the correct answers.
Step-by-step explanation:
Historians like Edwin Gibbon argue that the barbarian invasions were an important factor for the decline of the Roman empire as the citizens had become weak and couldn't defend their empire. They outsourced their duties to barbarian mercenaries, who later took over Rome. The spread of Christianity was another reason as the Christian belief that a better life existed in the afterlife sapped the Roman citizens desire to sacrifice their life for the empire.