Walbank offers the interesting idea, that the Romans didn't fall because of general or specific decadence, but because the Villa-based economy had become so self-sufficient that there was no need for the local movers and shakers to engage with a centralizing government, so they let it lapse until it was too late to put it back together. This is a simplification, but still a strand to be dealt with in further writing on the topic. Kind of an elephant in the room, in "Fall of Rome" discussions. He originally advanced this theory in 1947. ( )

Written in the 1940s and asks the question "Was ancient Rome a fascist state?"