alt Hacker NewsI recently read the book 'Barbarians' by Terry Jones (the ex-Python) and Alan Ereira. It suggested that, because the Romans were such a brutal bunch who levied high taxes, some people were happier after the collapse of their empire.
If anyone is interested in the rise and fall of empires, I strongly recommend the 'Fall of civilizations' podcast. It is a masterpiece of podcasting.
I think that was also a factor in the early success of the Islamic conquest. The Arabians initially imposed lower taxes and interfered less with local politics.