Worlds of Magic: Planar Conquest (UP)

This trophy description is misleading as you need 3 different cities not three races in a single city. There are 8 total races (known as Factions) in the game: High Men, Unhallowed, Grey Elves, Dark Elves, Draconians, Orcs, Dwarves and Myrodants. Start your game with Countless Neutral towns and you should easily have enough different races to choose from. Acquire 3 cities of different Factions and the trophy will unlock at the end of the turn.