Complex sentence: These people were primarily of Norwegian, Irish and Scottish origin, the Irish and Scots being mainly slaves and servants of the Norse chiefs according to the Icelandic sagas and "Landnámabók" and other documents.
Split into simpler sentences: These people were primarily of Norwegian, Irish and Scottish origin. Some of the Irish and Scots were slaves and servants of the Norse chiefs according to the Icelandic sagas and "Landnámabók" and other documents.