How did the hun contribute to the fall of the western empire?

As nomadic group of people which belonged to the region around the Capsian Sea, The Huns were responsibles for the Great Migration.

With brutal invasions of the regions sorrounding the Roman Empire, this tribe encouraged such migration, also known as the "Wandering of the Nations", which began between 300 and 700 CE, and was formed by the Alans, Goths, and Vandals among others.

They moved fast and were successful at battle. In 370 CE, they defeated and conquered the Alans, by 376 CE had pushed the Goths into Roman territory, and by 379 CE had pushed the people under the leadership of Athanaric into the Caucalands. These attacks produced a domino effect since many tribes, in their escape, sought refuge in Roman territory.

Such migration altered the conditions of roman society and eventually, after many insurrections and raids from these tribes, the Western Empire was weakened and collapsed.

the answer is d. selective incorporation. (apex)