The Decline and Fall Of The Roman Empire was written quite a few years after the occurrence, which naturally detracts from the authors vision and interpretation of the events.
Now, however, would be a perfect time for a new look at Rome's decline and fall as America is in that very situation in the 21st century.
The only problem is that rarely do major social upheavals register at the time. The precise moment when a society begins to decline is never marked by the society itself. It's usually assigned by future historians with the benefit of hindsight.
Never-the-less, American and European writers are in a unique position to knowingly describe and articulate the worldview held at the twilight of a civilization's existence.
Sad, but true.