About 3000 years B.C. many parts of Europe, including the British Isles, were inhabited by a people called Iberians who are still found in the North of Spain (later they were mixed with the Celts).
During the period from the 6th to the 3rd century B.C. a people called the Celts spread all over Europe from the east to the west. More than one Celtic tribe invaded Britain. From time to time these tribes were attacked and overcome by other Celtic tribes from the continent. There was probably never an organized Celtic invasion; for one thing the Celts were so fragmented and given to fighting among themselves that the idea of a concerted invasion would have been ludicrous.
The Celts were a group of peoples loosely tied by similar language, religion, and cultural expression. They were not centrally governed, and quite as happy to fight each other as any non-Celt. They were warriors, living for the glories of battle and plunder. They were also the people who brought iron working to the British Isles.
The use of iron had amazing repercussions. First, it changed trade and fostered local independence. Trade was essential during the Bronze Age, for not every area was naturally endowed with the necessary ores to make bronze. Iron, on the other hand, was relatively cheap and available almost everywhere.
Tribes of Scots crossed over to Ireland and settled there. Later the Scots returned to the larger island and in time the name of Scotland was given to the country.
