You know, the funny thing is that genetic study and little tidbits of archaeological evidence point to something of a confusion concerning the issue. It's been typically accepted that Indo-European migrations go east to west and are driven by war. The problem with this is that it shows two Celtic migrations (both out of the Caucasus like other European settlers), one engulfing the bulk of Europe and another piercing through the center while the Germans go north and Italics go south, basically leaving Celts to kick at their heels.
But there's more and more evidence to show that the Old European peoples (who are an archaeological puzzle concerning origins) were being ethnically consumed by the Celtic peoples starting along the Atlantic and moving inward until they end up nestled between the Germanics and Italics, which results in a conflict they show well in, but ultimately falter and fall back to the Atlantic coast.
The dating of such evidence though doesn't really mean that they came out at the same time as the others, rather that they came out early, made a roundabout course through the northern edge of Europe, settled on the coast, and then began assimilation once their linguistic and technological development hit a certain point, which just happens to start a while before the others launch.
This actually posed a problem for them, seeing that they experienced little conflict and what they did was against neolithic opponents, where the Celts were Bronze Age. So, to start, the Celts didn't kick much ass at all, given that they didn't develop warfare too extensively. For the longest time they made a good show through the use of numbers, but were pushed back close to modern limits.
With the domination by Germanics, Celts finally had a wake-up call. England was invaded and the Nordic sub-group of Germanics became the inheritors of the Iron Age, soon dominating Ireland (which did more than enough to impress the Nordic peoples and thus set the stage for their cultural preservation). It was King Malcolm I at the time who ruled over the bulk of Celts (the Scottish and Pictish mix we now know just as the Scots) and whipped them into shape, allowing them to push off repeated attempts at Nordic incursions and maintain the very existence of the Celtic peoples in any independent fashion.The only other group that came close to this was the Galati, who were practically stranded in the Middle East and became a powerhouse for centuries.
But yes, everyone in Europe came from the same locale. Then again, all mankind started in Africa. All life started in water. All existence started in some hot dot.
After a point, you're going to have to pick a difference if you're going to see one at all.
Go Aberdeen!
