Complex sentence: Those who settled in Cornwall and Wales made little long-term impact, however the Dál Riada settlers in Scotland eventually assimilated the Picts (a group of peoples who may have spoken a Brythonic language) who lived throughout Scotland.
Split into simpler sentences: Those who settled in Cornwall and Wales made little long-term impact. However, the Dál Riada settlers in Scotland eventually assimilated the Picts (a group of peoples who may have spoken a Brythonic language) who lived throughout Scotland.