In Celtic culture, what was the role of the Brehon?

Arohanui, do you not think the Celts destroyed the peoples who occupied, what is now Switzerland, France, Spain, Portugal, Romania, northern Italy, Bulgaria and similar areas, and the British Isles. There were stone age peoples in these places before the Celts came in and destroyed them by force. The Celts, cis/trans alpine Gauls also picked a fight with the Romans. The Celts started the Roman-Gallic wars. The Celts were not indigenous to the area. Please use a phrase like, 'the people who murdered the people who were there before them and stole their land'. Rather than indigenous.