You can sometimes tell a person's politics by asking them one question, "What do you think caused the fall of the Roman Empire?" Conservatives are quick to offer up that a large welfare state and dependence on foreign goods toppled the empire's economy. Liberals will cite that over expansion of the military weakened their defenses and they couldn't meed the demands of such a large geography.
Of course the smart asses, like myself, will always say invaders. Really though my answer to why Rome fell is because of the populace's apathy. They sat in their arenas entertaining themselves having slaves feed them their pampered lives while the political classes destroyed what was once a great civilization by squandering their once plentiful resources. Yes the people of Rome, the real stakeholders in it's greatness, are the ones to blame for it's government's failures.
We are no different.
"Ancient Rome was as confident of the immutability of its world and the continual expansion and improvement of the human lot as we are today." - Arthur Erickson