The decline of the roman empire was partly caused by

I'm not sure if there's multiple choice for this question, but this is my answer.

The decline of the Roman Empire was caused by:
 
- the invasion of nomadic tribes, such as the Barbarians. 
- economic instability.
- the rise of the Eastern Empire.
- over-expansion; the Romans had too much land to control and this is a big reason as to why they fell.
- government corruption and political instability.
- the arrival of the Huns.
- the spread of Christianity. 

The growth of the empire continued to increase their confidence.