Complex sentence: The story of the conversion of Iceland to Christianity which was first recorded by Ari Thorgilsson in the early 12th century "has been used to suggest that voluntary Christianization of an entire population was possible, without any link to a central power" (Nora Berend).
Split into simpler sentences: The story of the conversion of Iceland to Christianity was first recorded by Ari Thorgilsson in the early 12th century. All the same, the story "has been used to suggest that voluntary Christianization of an entire population was possible, without any link to a central power" (Nora Berend).