Answer:
This quote refers to the fact that the fall of the Roman Empire can not be linked to a single event, but rather relied on a number of cumulative events. For instance, many point to the invasion of Germanic Tribes from the North as causing the end of Rome. In reality, by that time Rome had undergone a series of internal and external crises such as Persian attacks in the East, civil upheaval surrounding the rise of Christianity, and the abuse of power by emperors and their followers. In the end, it was a little bit of all of these problems that contributed to the fall of Rome.
Generally it is true that loess deposits usually blanket an area in an even layer, although it should be noted that things like wind and rain patters can affect this distribution.
