Two Alliance races and two Horde races can become a Mage. They are:
-Humans
-Gnomes
-Orcs
-Undead
Like mages, Gnomes are seen as the more practical pick for Alliance Warlocks, due to their increase intellect for better stats, and Escape Artist helping in PvP, while the Humans Perception is a bit more limited.
Both Orc and Undead are great choices for a Warlock, though more of the Orcs racials are rendered useless compared to the Undead as Orc Warlocks can’t take advantage of Blood Rage or Axe Specialization, and Undead can still use Will of the Forsaken to great effect in PvP against other Warlocks.