Several causes operated in checking the growth of Norse power. One was the rivalry between the Danes and the Norwegians. Another was the consolidation of Scotland under Cinaeth Mac Ailpin. A third cause undoubtedly was the tenacious resistance of the "Celts." Had the Norsemen been as successful in Scotland and Ireland, Wales and Brittany, as they were in England and Normandy, Harald the Fair might have been the head of a new empire. The annals give a long list of pitched battles in Ireland, in some of which the invaders were victorious but for the most part they were defeated. Mr. Orpen ascribes their failure to the fact that the Irish were not politically centralised and were therefore harder to break down; yet he goes on to censure this defect in the Irish polity. Are we to conclude that it was a misfortune for Ireland and other countries that Ireland was not subjugated by the Scandinavian Heathens? As a matter of fact, it was under the personal command of the high-king, Aedh Finnliath, that the Irish resistance took a definitely successful turn. In 866, this king captured all the strongholds of the Norsemen in the northern half of Ireland; and from this time on, they made no settlements to the north of Dublin and Limerick. Olaf and Ivar, the two kings of Dublin, turned their arms against Britain. In 870, as already related, after a siege of four months, they captured the last stronghold of the northern Britons at Dumbarton. In recording the death of Ivar in 873, the Irish annals entitled him "king of the Norsemen of Ireland and Britain."