In fact, there are those who claim that the German tribes and peoples were all servants to the Gaelic speaking people wherever they might be found - rather like the old south where slaves were black and owners were white.
There was a massive German slave revolt against the Celtic owners. The Greeks reported on this although we have few details. The Celts had to relocate from areas North of the Danube to areas South of the Danube. These are the folks who moved into Italy and Switzerland. Julius Caeser in later centuries relocated some of them to what is now Belgium (Wallonia).
In a far earlier time the Celts were driven from Western Anatolia and from Bulgaria by Greek Barbarians (See: Homer). The seagoing Celts simply sailed South to the Mediterranean and set up colonies throughout the Mediterranean and up the Spanish coast.
It's a pretty cut and dried history once you understand that we are dealing with remnant refugee populations moving from one area to another, and eventually as far West as they could go.
Hey, that's us! 90% of all identifiable Celtic people live in the Americas or Australia these days.
If you have been following the "genetics studies" here on FR for the last year or two you know how unreliable they have proven to be. In fact, the only consistancy seems to be that the results of the genetics studies turn out to be whatever those doing the financing want them to be. It is truly scandalous, and while a great idea, is nothing we can hang our hat on at this time. Certainly nothing to use for rewriting history.