In 721 he fought against the rebellious Britons of Strathclyde, who had been subjugated a generation before. After sacking Alt Clut and perpetrating many massacres across the region, he forced the English language and culture onto the survivors, beginning their assimilation into wider Bernician society.
From 722 to 738 he fought a series of wars against Powys, Gwynedd and Ebrauc, sparked by his attempted reconquest of Caerbrauc. Instead, the Britons of the south united against him and fought back. Although he lost parts of Rheged and Dunutinga, he was able to preserve the remainder of his realm intact after suing for peace and agreeing to pay tribute.
Earnwine died in 745 and was succeeded by his son Æthelred.