Scottish aggression and Norwegian subjection
About a decade after Alexander II's death, his son and royal successor, Alexander III, came of age and took steps to continue his father's westward expansion. In 1261, the Scottish Crown sent envoys to Norway offering to purchase the Isles from Hákon. Once the Norwegians rejected the offer, the Scots are recorded to have lashed out against the Islesmen in a particularly savage attack upon the inhabitants of Skye. In 1262, the year after yet another failed attempt by the Scottish Crown to purchase the Hebrides, the thirteenth-century Hákonar saga Hákonarsonar reports that the Scots lashed out against the Islesmen in a particularly savage assault upon the inhabitants of Skye. Thus provoked, Hákon assembled an enormous fleet—described by the Icelandic annals as the largest force to have ever set sail from Norway—to reassert Norwegian sovereignty along the north and western coast of Scotland. In July 1263, this armada disembarked from Norway, and by mid August, Hákon reaffirmed his overlordship in Shetland and Orkney, forced the submission of Caithness, and arrived in the Hebrides.
According to Hákonar saga Hákonarsonar, Hákon was met in the region by Magnús Óláfsson, King of Mann and the Isles and Dubhghall himself. As the fleet made its way southwards, Hákon sent a detachment of vessels under the command of Dubhghall and Magnús Óláfsson to harry Kintyre whilst Hákon himself made landfall on Gigha. It is evident that Magnús Óláfsson and Dubhghall were tasked with bringing Aonghus Mór and Murchadh Mac Suibhne onto the king's side. The saga, and pieces of poetry embedded within it, glorifies the subsequent ravaging of Kintyre, suggesting that it was this rapaciousness that finally compelled Aonghus Mór and Murchadh to come into the king's peace. Certainly the saga reveals that these west-coast magnates duly submitted to Hákon, swearing oaths of allegiance, surrendering hostages into his keeping, and delivering the island of Islay into his control. The king is further said to have levied a tax of one thousand head of cattle upon the Kintyre headland, and a particular fortress—most likely Dunaverty Castle—is stated to have been surrendered to Hákon by an unidentified knight.
In early September, Hákon's fleet of Norwegians and Islesmen entered the Firth of Clyde. After negotiations between the Scottish and Norwegian administrations broke down, the saga identifies Magnús Óláfsson, Dubhghall, (the latter's brother) Ailéan, Aonghus Mór, and Murchadh, as the commanders of a detachment of Islesmen and Norwegians who entered Loch Long, portaged across land into Loch Lomond, and ravaged the surrounding region of the Lennox. According various versions of the saga, this contingent consisted of either forty or sixty ships—a considerable portion of Hákon's fleet. There is reason to suspect that this strike is evidence that the Norwegians and Islesmen were directing their fury at the territories of the powerful Stewart kindred. Furthermore, by penetrating into the Earldom of Lennox, and possibly striking further east inland, Hákon's adherents would have been encroaching into the Earldom of Menteith.
Meanwhile, at the beginning of October, Hákon's main force clashed with the Scots at Largs, and withdrew into the Hebrides. Once regrouped with the detachment of Islesmen, the saga records that Hákon rewarded his overseas supporters. Since Eóghan had refused to aid the Norwegians cause, Dubhghall and Ailéan were awarded his forfeited island territories. A certain Ruðri is stated to have received Bute, whilst Murchadh got Arran. Aonghus Mór—who is not identified as one of the beneficiaries—already enjoyed possession of Islay.
Although the saga declares that the Norwegian campaign was an overwhelming triumph, it seems to have been an utter failure instead. Not only did Hákon fail to break Scottish power, but Alexander III seized the initiative the following year, and oversaw a series of invasions into the Isles and northern Scotland. Recognising this dramatic shift in royal authority, Magnús Óláfsson submitted to Alexander III within the year, and in so doing, symbolised the complete collapse of Norwegian sovereignty in the Isles.
The Scots' retaliatory campaign against the Islesmen was evidently commanded by Alexander Comyn, Earl of Buchan, Uilleam, Earl of Mar, and Alan Hostarius. According to the fourteenth-century Gesta Annalia II, and the fifteenth-century Scotichronicon, it was these magnates who oversaw the Scots' ravaging of the islands. This source is corroborated by the thirteenth-century Magnúss saga lagabœtis, which states that Scottish forces invaded the Isles in the summer after Hákon's campaign, and forced the submission of Aonghus Mór and other adherents to the Norwegian cause. Evidence from the Scottish exchequer, concerning Uilleam's reception of monetary aid for commanding two hundred serjeants on behalf of the king in the Hebrides, also validates these accounts. Further evidence of a concerted campaign against Hákon's supporters is the record of Walter Stewart, Earl of Menteith assembling a royal fleet at Ayr, and of Uilleam taking twenty cattle from Kintyre.
Despite these retributory actions, the Scottish Crown was only partially successful in turning Clann Somhairle onside as Dubhghall stubbornly refused the recognise Scottish overlordship. Nevertheless, in 1266, almost three years after Hákon's abortive campaign, terms of peace were finally agreed upon between the Scottish and Norwegian administrations. Specifically, with the conclusion of the Treaty of Perth in July, Hákon's son and successor, Magnús Hákonarson, King of Norway, formally resigned all rights to Mann and the islands on the western coast of Scotland. In so doing, the territorial dispute over Scotland's western maritime region was finally settled.