I believe it was actually a result of a massive transgression of God's Law(s) that brought Rome down, albeit according to prophecy and plan however.
That's exactly what the Romans living at the time wrote.
Large numbers of citizens and non-citizens alike had abandoned worship of the Gods of their Fathers, Jupiter and the pantheon, in favor of the new superstitions of Christianity and Zoastraism.
Not even the threat of capital puishment was sufficient to stem this moral rot.
Romans at the time knew that this great evil would not go unpunished.