The Fall of the Roman Empire: a New History of Rome and the Barbarians by Peter Heather
I’ve read this before and read it again. I’m going to enjoy any book that uses lots of sources including archaeological evidence.
Heather suggests the main cause for collapse was the changing political systems of the Germanic world. By the 5th century AD this was increasingly large scale and able to deliver the disruption to the western Roman tax base. Once this had been disrupted sufficiently, in particular with the loss of North Africa, the state could not survive.
The eastern empire carried on for another 1000 years, but there was no successor to the western empire. For example, the Carolingian state only lasted for a few generations. The suggestion is that the Roman state had maintained a professional army which gave it more central cohesion, and once there was insufficient tax revenue to support this the empire died.
The division between the west and eastern empires is explained by bureaucratic necessity due to the poor communications of the times. I’ve always wondered how this could be stable. It also makes the point that in the 4th century a reigning emperor only visited Rome 4 or 5 times.