Which, as a few people commented, sounds a little fascistic, even for The Dark Knight.
I understand that the original name for the project from Frank Miller was the longer Batman & Superman Vs. The Master Race.
Which sounds a little clumsier but also a little less fascistic.
However, with the movie Batman Vs. Superman on the card, Warners rejected that title for fear of confusion in the marketplace, with a title that might see them appear to be allies and contradict the "Vs." in the movie
But either way, we do know that the Master Race in the title are the bad guys… as opposed to describing the superheroes.