As the Viking control of the west coast of Scotland advanced, Iona became part of the Kingdom of the Isles. Amlaíb Cuarán, King of Northumbria and Dublin, died in 981 while on Iona. Still, the island was sacked twice by his successors. On Christmas night 986 and again in 987. The ruling dynasty of Alba traced its origin to Iona, and the island thus became an important religious icon of the new kingdom. Many of its early kings are buried there. The kings of the Isles were at times vassals of the King of Norway, High King of Ireland, or the King of Scotland. By the 11th century they were nominally attached to the Kingdom of Norway, but in reality they were independent.