As Kil'jaeden prepared the Horde for its invasion of Azeroth, Medivh continued to fight for his soul against Sargeras. King Llane, the noble monarch of Stormwind, grew wary of the darkness which seemed to taint the spirit of his former friend. King Llane shared his concerns with Anduin Lothar, the last descendent of the Arathi bloodline, whom he named his lieutenant-at-arms. Even so, neither man could have imagined that Medivh's slow descent into madness would bring about the horrors that were to come.

As a final incentive, Sargeras promised to bestow great power upon Gul'dan if he agreed to lead the Horde to Azeroth. Through Medivh, Sargeras told the warlock that he could become a living god if he found the undersea tomb where the Guardian Aegwynn had placed Sargeras' crippled body nearly a thousand years before. Gul'dan agreed and decided that once the denizens of Azeroth were beaten, he would find the legendary tomb and claim his reward. Assured that the Horde would serve his purposes, Sargeras ordered the invasion to begin.

Through a joint effort, Medivh and the warlocks of the Shadow Council opened the dimensional gateway known as the Dark Portal. This portal bridged the distance between Azeroth and Draenor, and it was large enough that armies might pass through it. Gul'dan dispatched orc scouts through the portal to survey the lands which they would conquer. The returning scouts assured the Shadow Council that the world of Azeroth was ripe for the taking.

Still convinced that Gul'dan's corruption would destroy his people, Durotan spoke out against the warlocks once more. The brave warrior claimed that warlocks were destroying the purity of the orcish spirit and that this reckless invasion would be their doom. Gul'dan, unable to risk killing such a popular hero, was forced to exile Durotan and his Frostwolf Clan into the far reaches of this new world.

After the exiled Frostwolves charged through the portal, only a few orc clans followed. These orcs quickly set up a base of operations within the Black Morass, a dark and swampy area far to the east of the kingdom of Stormwind. As the orcs began to branch out and explore the new lands, they came into immediate conflict with the human defenders of Stormwind. Though these skirmishes usually ended quickly, they did much to illustrate the weaknesses and strengths of both rival species. Llane and Lothar were never able to gather accurate data of the orcs' numbers and could only guess at how great a force they would have to contend with. After a few years the majority of the orcish Horde had crossed into Azeroth, and Gul'dan deemed that the time for the primary strike against humanity had come. The Horde launched its full might against the unsuspecting kingdom of Stormwind.