What is the reason for the invasion of the barbarians into the Roman Empire?

In the period of 3-5 centuries, the Great Migration of Peoples took place, during which numerous tribes of the Huns moved to the east and pushed the tribes of the Germans, and they, in turn, moved even further to the west. This is how virtually all the tribes of Europe began to move. The borders of the western Roman Empire began to crack with the arriving barbarians. In addition, in the 5th century, it suffered greatly from the invasion of the Huns, so the power of Rome was finally undermined. In this connection, it became an easy prey for the barbarians, who immediately rushed in a stormy stream to seize the weakened empire.