The Orcs originated from another world, where the majority were bloodthirsty warriors driven by strife. However, their Warlocks remained aloof, devoted to the research of magic. The Warlocks noticed a rift between the dimensions and, after many years, opened a small portal to another world. One Warlock explored and found a region, whose Human inhabitants called it "Azeroth", from which the Warlock returned with strange plants as evidence of his discovery.
The Orcs enlarged the portal until they could transport seven warriors, who massacred a Human village. The platoon brought back samples of good food and fine workmanship, and a report that the Humans were defenseless. The Orcs' raiding parties grew larger and bolder, until they assaulted Azeroth's principal castle. However, the Humans had been training warriors of their own, especially the mounted, heavily-armed Knights. These, assisted by Human Sorcerors, gradually forced the Orcs to retreat through the portal, which the Humans had not discovered.
For the next fifteen years, one faction of Orcs demanded that the portal be closed. However a chief of exceptional cunning realized that the Humans, although out-numbered, had prevailed through the use of superior tactics, organization, and by magic. He united the clans, imposed discipline on their army and sought new magics from the Warlocks and Necromancers. Their combined forces were ready to overthrow the Humans.