Warcraft: The Official Prequel Novel — Christie Golden

In the world of Draenor, the strong and fiercely independent Frostwolf Clan are faced with increasingly harsh winters and thinning herds. When Gul'dan, a mysterious outsider, arrives in Frostfire Ridge offering word of new hunting lands, Durotan, the Clan's chieftain, must make an impossible decision: abandon the territory, pride and traditions of his people, or lead them into the unknown.
An original tale of survival, conflict and magic that leads directly into the events of Warcraft, an epic adventure from Legendary Pictures and Universal Pictures, based on Blizzard Entertainment's global phenomenon.