The reasons for Somairle's invasion of Scotland are uncertain. One possibility is that he was renewing his support for the sons of Máel Coluim. Another possibility is that he was attempting to conquer the southwest part of Scotland that may have only recently fallen under Scottish royal authority. This region had previously been occupied by the Gall Gaidheil, a people of mixed Scandinavian and Gaelic ethnicity, like Somairle himself. There is reason to suspect that this region was lost to the Scots upon the collapse of Máel Coluim's rebellion, and afterwards doled out to powerful Scottish magnates in the context of Scottish consolidation. Somairle may have also invaded the region in an attempt to counter a perceived threat that the Scots posed to his authority in the Firth of Clyde. The fact that the battle is said to have been fought at Renfrew, the seat of one of Walter's lordships, could indicate that he was a specific target.