Answer:
Poor economy
Explanation:
The decline of Rome started in the 3rd Century, but then there was a welfare during Constantine and Diocletian. Still, after the Empire was divided in 395 it was impossible to preserve the independence of the Western Empire. There wasn't enough resources and money to pay the army, so the mercenaries turned against country. It was just a question of the time when the Empire will collapse and that finally happened in 476.
