Board Thread:Naruto Discussions/@comment-3279282-20140828133937/@comment-1894786-20140829012530

Jashin Uchiha wrote: Did Hagoromo summon himself to Kaguya's dimension? or Teleport there and summon the kage?

Nope. He called forth the ghosts of every previous Kage in history (Damned if I know how) and all of them combined their powers with Hagoromo and the reincarnated Hokage to summon Team 7 from Kaguya's dimension.