The correct answer is the first one in order: the instability of foreign trade.
The Fall of the Roman Empire is also called Fall of The Western Roman Empire and it was the process in which the Empire failed to enforce its rule and its huge territory was divided into several sovereignities.
Theodosius death, leaving two incapable sons, resulted in a collapsing the field army and also several civil wars which weakened the Roman Empire and helped to bring it down.
