Dal Riada is an interesting case of a kingdom which migrated with king and populace. Originally sited in Atrim in Ireland, they moved to the west of Scotland and settled land there, eventually becoming one of the main incomer colonists of the Scots landscape, along with Norse (and other Vikings), and the ever land-hungry men of England -- the Angles.
According to these lists the Dal Riada kings moved to Scotland in the early fifth century, led by Fergus Mor, with Angus Fert and Eochaid Muinremar as their first Scots kings. From the scant remaining records they appear to have intermarried both with Irish lineages, and with Pictish princesses. In the early seventh century Domnall Brecc married the daughter of the then-king of Northumbria (whose mother had been a Pictish princess). It was also at the time that their links to Ireland finally withered, with the Battle of Mag Reth in which the Dal Riada were defeated by the Ui Neill.