I've been reading that the Romans were a society with low taxes, usually ranging from 1 to 3%, which is a pretty huge difference when compared with the feudal kingdoms and the taxation of the Emperor Justinian I.

The only thing I don't understand is why riots and civil wars are so common among slaves and commoners after the period when the empire stopped expanding. I do not know if it's revisionism's fault if we have the idea of ​​a perfect Roman Empire, or even because Byzantine Empire was really badly run, corrupt and full of political conspiracies compared to its ancient equivalent. Not only that, but the Byzantine agriculture also appeared to be well "oppressive" and not as mechanized as the feudal agriculture of the second half of the Middle Ages, so maybe the Byzantines never abolished slavery because of that. The Arabs and the Ottomans were able to take support from the byzantine population in exchange for low taxes and religious tolerance.

When I read a bestseller in my country he cites the "Framing the Early Middle Ages: Europe and the Mediterranean, 400-800" by Chris Wickham, mentioning that barbarians had found support from the rural population of the Roman Europe in their invasions. It seems that the barbaric domination could put an end to taxes charged that kept the legions standing armies and their "fat bureaucrats" (although I learned that Spain's Ostrogoths also charged a lot of taxes when the muslims invaded Al Andalus)

My question is: high taxes were actually a cause of discontent of the people? Maintain a standing army (ancient roman and even byzantine) was that expensive? Maybe that's why the first post-classical standing army first appeared in the late Middle Ages?

Ermatingers conclusion is interesting.

"But who benefited from Rome’s fall? By examining the social and political groups from the bottom up, a fuller picture can be gained. The peasantry and poor clearly did not benefit from Rome’s collapse. These individuals still paid taxes, worked the lands, and coped with constant attacks and demands. The urban poor clearly suffered, losing their grain dole, games, and, often, their personal safety. Above them the merchants clearly did not benefit from Rome’s collapse. Without imperial protection, trade and commerce suffered, becoming more localized. Long-distance trade, with the potential of exotic items and fantastic rewards, diminished. As society changed, the market for rare or expensive merchandise for numerous wealthy patrons diminished while greater risks to the merchants accrued. The elite may have benefited, positioned as local magnates controlling the regions politically, socially, and economically. By using their landed estates with military retainers the elites often became quite powerful, perhaps more so without imperial checks and balances. At the same time these individuals were often in danger, since without imperial protection large-scale invasions could destroy their property and power. The church gained from the collapse of Rome, and promoted itself as the protector of society, often against the Arian Germanic chieftains. With the imperial collapse, the church became the most important organization in society. The German tribes also benefited from Rome’s fall. As the new power they controlled the resources, population, and land."

My conclusion would be: Winners were in the short term villa owners, then more long term Germanic tribal lords and the Church winning in the historical long run, as they eventually made the Arian Germanic tribes Roman Catholic starting with the Franks.