Through Medivh, Sargeras used the warlock's magic to communicate with draenor and the Horde. He promised Gul'Dan 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 declared 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.

As the forces of Azeroth and the Horde clashed across the kingdom, internal conflicts began to take their toll on both armies. King Llane, who believed the bestial orcs to be incapable of conquering Azeroth, contemptuously held his position at his capital of Stormwind. However, Sir Lothar became convinced that the battle should be taken directly to the enemy, and he was forced to choose between his convictions and his loyalty to the king. Choosing to follow his instincts, Lothar stormed Medivh's tower-fortress of Karazhan with the help of the wizard's young apprentice, Khadgar. Khadgar and Lothar succeeded in vanquishing the possessed Guardian, whom they confirmed to be the source of the conflict. By killing Medivh's body, Lothar and the young apprentice banished the spirit of Sargeras to the abyss. As a consequence, the pure, virtuous spirit of Medivh was also allowed to live on ... and wander the astral plane for many years to come.