How did Rome become politically unstable?

There are a plethora of reasons why Rome, one of history's longest-lasting and most powerful empires, finally fell.  Although the reasons and their level of importance are highly debated among historians, most agree that there were certain factors that clearly led to the Roman empire's demise.

Rome had always struggled against invasions by Germanic tribes, but in 476 the Roman emperor Romulus Augustulus was deposed by Germanic leader Odoacer.  After this happened, no Roman emperor ever again ruled from a post in Italy.

Rome also began to struggle economically due to its constant wars and overspending on outside conquests. Its over-expansion made it difficult to administer and run the empire across such great distances, while military overspending emptied its treasury.  These problems were exacerbated by the rampant corruption that existed in the Roman government.  Roman citizens began to lose trust in their leadership, setting the stage for civil revolt.