The whole thing was part of the Voelkerwanderung, a complex movement reaching via the Steppes all the way to China.
Part of. There are various cultural and other things going on. There were similar barbarian incursions all thru out Roman history. They managed for at least 1000 years to manage the threat. The Eastern Empire did for just over an additional 1000 years afterward. Rome died in stages not in a massive Gotterdamerung.