The prosperous fortunes of Somerled at length inflamed his ambition. He had already attained to great power in the Highlands, and success inspired him with the desire of extending it. His grandsons having formerly claimed the earldom of Moray, their pretensions were now renewed, and this was followed by an attempt to put them in actual possession of their alleged inheritance. The attempt, however, failed. It had brought the _regulus_ of Argyll into open rebellion against the king, and the war appears to have excited great alarm amongst the inhabitants of Scotland; but Somerled, having encountered a more vigorous opposition than he had anticipated, found it necessary to return to the Isles, where the tyrannical conduct of his brother-in-law, Godred, had irritated his vassals and thrown everything into confusion. His presence gave confidence to the party opposed to the tyrant, and Thorfinn, one of the most powerful of the Norwegian nobles, resolved to depose Godred, and place another prince on the throne of the Isles. Somerled readily entered into the views of Thorfinn, and it was arranged that Dugall, the eldest son of the former, should occupy the throne from which his maternal uncle was to be displaced. But the result of the projected deposition did not answer the expectations of either party. Dugall was committed to the care of Thorfinn, who undertook to conduct him through the Isles, and compel the chiefs not only to acknowledge him as their sovereign, but also to give hostages for their fidelity and allegiance. The Lord of Skye, however, refused to comply with this demand, and, having fled to the Isle of Man, apprised Godred of the intended revolution. Somerled followed with eight galleys; and Godred having commanded his ships to be got ready, a bloody but indecisive battle ensued. It was fought on the night of the Epiphany; and as neither party prevailed, the rival chiefs next morning entered into a sort of compromise or convention, by which the sovereignty of the Isles was divided, and two distinct principalities established. By this treaty Somerled acquired all the islands lying to the southward of the promontory of Ardnamurchan, whilst these to the northward remained in the possession of Godred.