They're sneaking over the alps with elephants to get us?!? Those barbarians!!
OR
OR MAYBE- and I'm just spit balling here...
Maybe Rome fell because the underpinnings of their economy depended on slave labor- specifically sending their military out to a new area, conquering it and then importing those people as a new round of slaves.
But when the nativist movements hit Rome in the 2nd century, they stopped conquering new land and importing yet more slaves and tried to depend on Romans to do the slave work. Which, shockingly, didn't work out.
So, Rome was unable to feed it's people, unable to rebuild it's armies, the rich kept sucking money out of the economy by not paying their taxes and pushing more and more of the tax load on the increasingly shrinking middle class and the poor.
Which meant their infrastructure fell more and more apart. Which forced the income gap to widen even further decade after decade.
Eventually the Emperor moved the capital from Rome to Constantinople, which was a more profitable and prosperous part of the empire.
With the shift in power to the east, Rome became internally more and more corrupt. It was a culture of "f**k you, I'm getting mine." in full effect.
With rampant corruption in their leadership, Romans lost all trust in their political figures. This further reinforced a decline in civic pride.
Additionally, their traditional moral social structures were being eroded as well with the advent of a new religion- Christianity.
When the people who staffed the legions stopped wanting to be in the legions because "f**k you, Rome, you're not helping me I'm not helping you" the corrupt politicians turned to mercenary forces.
Once you start buying troops to fight your wars, it's over.
But, yeah, I mean IT COULD BE that the cheap labor being imported was the problem.
(it wasn't)
