From the introduction:
Mankind, also called Men and sometimes Humans, are a race of intelligent, mammalian humanoids dominant in the Old World. The race of Men were one of the last intelligent peoples of the Warhammer World to become civilized. However, they are now one of the most powerful and populous species spread across the globe and might be considered the dominant intelligent race of the Warhammer World since the civilizations of the High Elves and the Dwarfs entered their mutual states of decline. Men are the chief devotees of the Imperial god Sigmar, as well as the primary opponent of Chaos' continued incursions into the Old World. In a severe grip of irony however, Mankind is also amongst the Dark Gods' greatest and most numerous servants.