Complex sentence: The Isle of Islay had belonged to Clan MacDonald whose clan chief was Sir James MacDonald, 9th of Dunnyveg, a nephew of Sir Lachlan Mor Maclean.
Split into simpler sentences: The Isle of Islay had belonged to Clan MacDonald. The clan chief was Sir James MacDonald, 9th of Dunnyveg, nephew of Sir Lachlan Mor Maclean.