¬ coins manipulation in order to increase the wealth of the state : the empire created more and more coins with less and lessvalue that generated two consequences :
¬ a constant depreciation of money.
¬ the surplus of money were used for military and public services, not redistribute to peoplein the society so they had less and less money, but continued to pay big taxes, and prices continued to increase. So there was inflation and a conflict appeared between thesociety and the state.
The historian James Burke says that the Roman Empire was declining since its beginning : it couldn’t work on the long term because there was nobudget system, and the richness of Rome only came from booty and taxes so when the expansion of the Empire ended there was no booty no more and taxes, that generated populationpoverty, were the first source of richness.
There is another theory that says that there was no real end in the Empire : it continues to exist under another form than The bigEmpire until the Arabian conquests in the 7th century that disturbed the trade in Mediterranean Sea and generated the decline of European economy
If we suppose that therewas a decline of the Roman Empire, no doubt it was because of the military system : they took lots of young people from farms so there were less and less people for theagriculture, so less and less fields, and the agriculture declined. Because of the Barbarian treat, army also use too much money toward its resources, that became poorer andpoorer (mines, food from rivers…).
Another reason can come from the barbarian invasion in 455 : a lot of people left the city and all the richness was stolen by barbarians.