The Chain of Loyalty is one of the most sacred pieces of the Treasure of Thundera. It is said that if the chain is broken, the ThunderCats will begin to fight amongst themselves; according to Jaga, it is deceptively delicate.
The chain appears in the Book of Omens and on the chain are the images of the current ThunderCats. When the treasure was scattered across New Thundera, the chain found itself in the Mountains of the Moon. It was almost claimed by Mumm-Ra, but it was accidentally broken by Lion-O with the Sword of Omens. Once broken, the ThunderCats indeed began to fight one another until the chain was repaired with the magic of the Sword of Omens.