Are you thinking of the World Powers and the Revelation book as interpreted by (mostly) the JWS and (some) other fundamentalist religions?
It kinda makes sense, because these 'newer' religions were mostly formed in the USA, the mythological explanations seem to revolve around their own ancestors and religions, so the Mongols just didn't figure in. It's too far away, too 'foreign' to American culture, to have been incorporated into the Western system of myth as one of the 'world powers'. The Mongols, who are they? Oh, wasn't he some big warrior dude? Or was that Star Trek? KHA-A-A-NNNN!
:))