Complex sentence: The Clan Johnstone also had a long feud with the Clan Moffat who were another Scottish border clan who were raiders and reivers, and conducted long-running feuds with their neighbours.
Split into simpler sentences: The Clan Johnstone also had a long feud with the Clan Moffat who were another Scottish border clan. The Moffats were raiders and reivers, and conducted long-running feuds with their neighbours.