Where did England and Scotland come from?
The short answer is that these nations were forged out of the fire of the Viking invasions that engulfed Britain in the 9th and 10th centuries. By the time it was over, the seven Anglo-Saxon kingdoms had become England and what became Scotland was emerging from the wreckage of the kingdom of the Picts, Dál Riata and the British kingdom of Strathclyde.
We’ve already seen how the Vikings conquered Northumbria, East Anglia and eastern Mercia which became the Danelaw in England. Ivar the Boneless also conquered the British kingdom of Alt Clut and the Norse overran Dál Riata and created the Kingdom of the Isles in its place. The Orkney Islands and northern Scotland were conquered and ruled for centuries by the descendants of the Norse. The Picts disappeared and were absorbed by the Gaelic Scots.
It is easy to see how history could have taken a different course. Suppose that Guthrum had defeated Alfred and England had become Daneland. If the Vikings had never invaded Britain, would the Kingdom of the Picts have survived? What if the Old North had survived intact like Wales as a British kingdom between England and Scotland?