In Chapter 4 of The Isles by Norman Davies, he writes:
One effect of the Northumbrian advance was to split British territory in Caledonia into two. By the eighth century at the latest, the southern chunk that was soon to be called Cumbria, i.e., a second Cymru, was completely separated by Bernician territory from the British kingdom of Strathclyde, with its capital at Dumbarton
But I'm unable to realize what does he mean by this point or what is so significant in what he said. I guess he wants to say that two celtic kingdoms were separated by an anglic kingdom which led to their languages and culture diverge with Cumbria more like Welsh and Strathclyde more like Scots. Is this right ?