One of the most widely accepted causes - the influx of a barbaric horde - is discounted by some who feel that mighty Rome, the eternal city, could not have so easily fallen victim to a culture that possessed little or nothing in the way of a political, social or economic foundation. They believe the fall of Rome simply came because the barbarians took advantage of difficulties already existing in Rome - problems that included a decaying city (both physically and morally), little to no tax revenue, overpopulation, poor leadership, and, most importantly, inadequate defense. To some the fall was inevitable.

Fall of the Western Roman Empire, Ancient History Encyclopedia

What is the historical context of Document #1?

The historical context is that Rome destroyed itself.

Explanation:

From this document we can see that the author seems to think that no other group of people, especially not culturally inferior one, was able to take down Rome, but instead it was Rome itself that was the cause of this collapse. This standpoint is as controversial as the other one, as both have pros and cons when it comes to their stances.

Most probably, the cause for the fall of the Roman Empire were both, not just one of this causes. In the same time while the Roman Empire started to face internal difficulties it was not given time to recover but instead it was further damaged by the barbaric hordes of the Avars, Huns, Vandlas, Goths and others.

What the author states though that Rome could not have been defeated by any other people that are culturally, economically, and politically inferior to them is probably not on spot. A good example for this are the Huns who managed to defeat the Roman Legions and entered the lowlands of northern Italy. From still unknown reasons they stopped and returned back though the chances were that they will mange to invade Italy and conquer Rome, but it seemed like they didn't wanted too deal with it.