Scandinavia (contd.) Norway OTL was involved in dynastic civil wars for nearly a century from 1130 on. Pretenders, all claiming descent from Magnus III Barelegs, who had died in the first decade of the century, were taken up by internal factions within the country. Sometimes the Danes or Swedes would support a candidate.
Previously, Norway was strong, and its king, Sigurd, had been on a successful crusade before 1110. If you butterfly away king Magnus's adventures in Ireland, you don't get the pretenders who came from there, and Norway remains a significant Northern power with a strong fleet. Your call which direction it is sent.