What Role did the Huns and the Visigoths play in the fall of Rome?

Throughout the decline and "fall" of Rome, the city was sacked numerous times by the Huns and Visigoths. 

The Hun homelands are not clearly known but were somewhere in the steppes of South Eurasia. They began a slow push westward and in 376 their attacks on the Pontic Steppes forced thousands of Goths and other ethnic groups into the Roman Empire. In 380, the Roman Empire granted some groups of Huns allegiance and validity as ...

Throughout the decline and "fall" of Rome, the city was sacked numerous times by the Huns and Visigoths. 

The Hun homelands are not clearly known but were somewhere in the steppes of South Eurasia. They began a slow push westward and in 376 their attacks on the Pontic Steppes forced thousands of Goths and other ethnic groups into the Roman Empire. In 380, the Roman Empire granted some groups of Huns allegiance and validity as federati- mercenaries who were allowed to live on Roman land in exchange for their fighting power. The relationship between the Huns and the Roman Empire was complicated, as they had caused mass migrations into Rome, attacked the Empire itself, and at the same time were hired by the Empire to fend off other groups.

The Visigoths were a large group of a number of northern European Germanic ethnic groups, who attacked the Roman Empire and the city of Rome in the third and fourth centuries. In 410, the Visigoths under Alaric attacked Rome by surrounding the city and capturing the port. Rome was utterly devastated, and we now refer to this as the Sack of Rome by the Visigoths. 

If any two groups were instrumental in the decline of Rome, we could say it is the Huns and the Visigoths.