The brutal orcs of orgrimmar are brutal conquerors, stopping at nothing to rule the world.

After the lich kings powers dwindled, some of the scourge regained their minds, renaming their selves forsaken, they will not stop until the scourge is destroyed.

The cow like tauren worship the earth mother, and after they became allies of the horde, they found a final home.

The trolls of echo isle are strong shadow hunters, using voodoo to stalk their enemies through the forest. After the zandalari grouped the trolls into a single empire, the darkspear refused, saying the horde was their true home.

During the cataclysm, the goblins of kezan were forced out of their home by deathwings eruption of mount kezan. They found a home in the horde when they encountered thrall on the echo isles.

The high elfs of quel'thelas were originally part of the alliance, but left for unknown reasons. They joined the horde so they could live the amani trolls  assault on their home.