half century. The kingdom was than sundered due to the actions of Somerled whose sons inherited the southern Hebrides whilst the Manx rulers held on to the "north isles" for another century. The origins of both Godred Crovan and Somerled are obscure—the former may have been an Uí Ímair dynast from Islay, the latter married a Crovan heiress. Thus it is clear that although there were competing factions in play, the Hebrides and islands of the Clyde were essentially under the control of rulers of Scandinavian origin from "at least the late tenth century" until the emergence of the kingdom of Scotland and its 13th-century expansion into the west. Relations with Pictland, Strathclyde and Alba The early Viking threats may have speeded a long term process of gaelicisation of the Pictish kingdoms, which adopted Gaelic language and customs. There was a merger of the Gaelic and Pictish crowns, although historians continue to debate whether it was a Pictish takeover of Dál Riata, or the other way around. This culminated in the rise of Cínaed mac Ailpín in the 840s, who brought to power the House of Alpin who were leaders of a combined Gaelic–Pictish kingdom for almost two centuries. In 870 Dumbarton was besieged by Amlaíb Conung and Ímar, "the two kings of the Northmen", who "returned to Dublin from Britain" the following year with numerous captives. Dumbarton was the capital of the Kingdom of Strathclyde and this was clearly a major assault which may have brought the whole of mainland Scotland under temporary Ui Imair control. Three years earlier Vikings had seized Northumbria, forming the Kingdom of York and subsequently conquered much of England except for a reduced Kingdom of Wessex, leaving the new combined Pictish and Gaelic kingdom almost encircled. Amlaíb and his brother Auisle "ravaged the whole of Pictland and took their hostages" and later occupied this territory for a protracted period. The 875 Battle of Dollar was another major setback for the Picts/Scots. In 902 the Norse suffered a serious reverse in Ireland losing control of Dublin and this seems to have intensified attacks on the emerging kingdom of Alba. A year later Dunkeld was attacked and Ímar, the "grandson of Ímar" was killed in battle with the forces of Constantine II in mainland Scotland. In the late tenth century the battle of "Innisibsolian" was won by Alban forces over Vikings. Yet these events were setbacks