Which event do historians say marks the end of the Western Roman Empire?

To many historians, the fall of the Western Roman Empire in the 5th century CE has always been viewed as the end of the ancient world and the onset of the Middle Ages, often improperly called the Dark Ages, despite Petrarch’s assertion. Since much of the west had already fallen by the middle of the 5th century CE, when a writer speaks of the fall of the empire, he or she generally refers to the fall of the city of Rome. Although historians generally agree on the year of the fall, 476 CE, they often disagree on its causes. English historian Edward Gibbon, who wrote in the late 18th century CE, points to the rise of Christianity and its effect on the Roman psyche while others believe the decline and fall were due, in part, to the influx of 'barbarians' from the north and west.  

Whatever the cause, whether it was religion, external attack, or the internal decay of the city itself, the debate continues to the present day; however, one significant point must be established before a discussion of the roots of the fall can continue: the decline and fall were only in the west. The eastern half - that which would eventually be called the Byzantine Empire - would continue for several centuries, and, in many ways, it retained a unique Roman identity.

it refers to race, i am pretty sure this was a popular term in nazi germany or something.