I misunderstood your post... not being too lucid on the finer points of Roman and German history. My apologies.
The Goths are a great example of this. Pushed from the East by the invading Huns, and denied suitable territory and protection inside the Empire, they re-forged their confiscated weapons and took on Roman legions and tore them to pieces, then went on a rampage all over nortern Greece. Eventually making their way to the south of Gaul, the Visigoths founded a Christian Empire in Hispania and part of Gaul.
And it is not without reason the Romans called Attila the Hun "The Scourge of God." Rome fell because the people, especially the nobles, cared more for the material wealth they created than for the discipline and honor that made that wealth possible.