Originally Posted by
rda
A realistic way to do it in the lore: the Alliance destroys the Horde from the military point of view, winning everything. They spare to what remains of the Horde their lives and allow them to live under the rule of the Alliance, scattering them from Orgrimmar and similar centers of former Horde power. The players belong to the part that has been spared. (Many of their in-game characters would actually welcome it, because the Horde did little good, it was bloody evil 90% of the time, but that's beside the point, it doesn't matter.)