Pre-Brythonic Armorica includes the ancient megalith cultures in the area and the Celtic tribal territories that existed before Roman rule. After the collapse of the Roman Empire, large scale migration from the British Isles led to the foundation of British colonies linked initially to homelands in Cornwall, Devon, and Wales. The various independent petty Breton states later developed into a Kingdom and then a Duchy of Brittany, before it was unified with France to become a province. After the French Revolution Brittany was abolished as an administrative unit, but continued to retain its distinctive cultural identity. Its administrative existence was reconstituted, in reduced size, as the Region of Brittany in the mid-20th century.