How did Rome Fall?

Most history scholars agree that the year 476 AD was the official date of the fall of the Roman Empire.  This was when a Germanic leader named Odovacar deposed the last Roman emperor, Romulus Augustus.  Although this marked the official end of the empire, the forces that led to the final collapse had been at work since at least the third century.
Late in the third century, Emperor Diocletian divided the Empire into two parts: the Western Empire based in Italy and the Eastern Empire based in what is now known as Constantinople.  At first, this made the empire easier to govern and seemed to make sense, but as time went on, the two empires became less of a cohesive unit and more like two separate kingdoms, making each more vulnerable. 
During this time, invasions by barbarian groups increased in frequency and savagery.  The Huns were spreading terror through Eastern Europe, and the displaced populations of these areas felt they had nowhere else to go. They began to set their sights on Rome.  At first, they sought refuge, but as conditions for them deteriorated, it became a mission of conquest.  In 410 a Visigoth ruler known as Alaric sacked the city of Rome, and in 455, Rome was raided again, this time by the Vandals.
The vastness of the empire and its obsession with conquering new lands had stretched the army dangerously thin and completely depleted Rome's finances.  The empire's size made it nearly impossible to govern effectively, and government corruption was rampant.  The reasons for the fall of Rome were primarily economic and political.  Rome's downfall in 476 AD was the culmination of factors that had been at work for at least one hundred years.