How did the Vandals potentially cause the direct collapse of the Roman Empire?

Vandals and other "barbarian" groups had long been blamed for the fall of the Roman Empire by writers and historians.

Explanation:

on the morning of  july 21,  1861, general mcdowell ordered the  unionarmy to attack. it was on this hill that  confederate  colonel thomas jackson and his forces held back theunion  troops.