The were joined by the Allemanni – they gave the name the Germany in the French language ‘ Allemagne’, in Spanish Alemania and in Portuguese Alemanha, it translate to “all men”, most likely revering to a combined confederation.
The collapse of the Roman Empire was partly due to the fact that a weakening empire could no longer control it borders and this led to more serious invasions and eventually these tribes took over all of the Roman Empire with the exception of the eastern part.
The Sallii moved from the River IJssel in what is now modern Brabant, Flanders, northern, France and the Rhineland in Germany.
While there certainly was a lot of violence involved, evidence indicates that in most situations the newcomers (often less than 10% of the total local population, sometimes as low as 2%) rapidly integrated with the local population.
This in particular was the case where the newcomers settled in Celtic lands; they very rapidly replaced the local culture and language.
At the time of the initial migration (between 500 and 300BCE), the region had become under the influence of the Celts, who had moved in from the east, somewhere between 600 and 300 BC.
It is believed that the Germanic tribes that evolved from here mixed in with the early farmers and with the newly arrived Celts.
At the time the Romans arrived the Germanic tribes of the Cimbri and the Teutones had reached southern France and during their annual raiding campaigns even ventured into Italy and Spain.
By that time the Romans had conquered the Mediterranean and started to move north.
together was the rather small tribe of the Tubanti (Twente) they stayed more or less in their original lands possibly for over a thousand years.
The Lombards were a reasonable late comer and started to take over several parts of northern Italy around 600AD.
Frankenland in modern Germany is an example of a rather rapid transformation.