Board Thread:Theories and Speculation/@comment-31099706-20170510101001/@comment-734582-20170512171442

OnlineLurker wrote: 1. Afaik that wasn't explained, but i think they're defected clan members. kaguya was the otsutsuki clan leader, so it shouldn't be surprising they know her. Well it's possible there are other clans of the Otsutsuki species out there, and Kinshiki and Momoshiki defected to the Home World clan. We know for a fact that the Otsutsuki have a homeworld. We know Momoshiki and Kinshiki spent a millenium before coming to Earth. We've seen that they went to a planet with a dead Shinju and no signs of civilization, so it's likely it wasn't even the Otsutsuki homeworld.

With that information, it's likely that some sort of interplanetary war or rebellion was brewing which eventually brought the Otsutsuki down.

Anyway, they were considered a greater threat, not a greater power.