The fall of the roman military power

[L.Valerius Gaudentius]

My understanding of the finances of empire is that the armies of the early and middle Republic were only paid minimally, and were conscripted. These two factors make it much easier to raise very large armies. In the late Republic the armies were becoming professionalized, and paid accordingly. Of course, there were wealthy and accessible lands to conquer and loot, which helped ease any difficulties in paying an army. In the later Empire, the armies were pretty much fully professional, which demanded greater pay, and the supply of easily plundered lands had all flowed into the Empire, which was a great incentive to outsider attackers, and meant the armies were not supposed to plunder these properties. This would make it difficult to raise or maintain armies in the way the Republic did.

I think in the same way, the Republic armies were paid less than the Late Empire armies. In spite of this, in the Republic times there were more accesible lands to conquer, but in the Late Empire it wasn´t that lands. However, this isn´t the main problem.