Kil'jaeden and the Shadow Pact
Around the time of Medivh's birth on Azeroth, Kil'jaeden the Deceiver sat and brooded amongst his followers within the Twisting Nether. The cunning demonlord, under orders of his master, Sargeras, was plotting the Burning Legion's second invasion of Azeroth. This time he would not allow any mistakes. Kil'jaeden surmised that he needed a new force to weaken Azeroth's defenses before the Legion even set foot upon the world. If the mortal races, such as the night elves and dragons, were forced to contend with a new threat, they would be too weak to pose any real resistance when the Legion's true invasion arrived.
It was at this time that Kil'jaeden discovered the lush world of Draenor floating peacefully within the Great Dark Beyond. Home to the shamanistic, clan-based orcs and the peaceful draenei, Draenor was as idyllic as it was vast. The noble orc clans roamed the open prairies and hunted for sport, while the inquisitive draenei built crude cities within the world's towering cliffs and peaks. Kil'jaeden knew that Draenor's denizens had great potential to serve the Burning Legion if they could be cultivated properly.
Of the two races, Kil'jaeden saw that the warrior orcs were more susceptible to the Legion's corruption. He enthralled the elder orc shaman, Ner'zhul, in much the same way that Sargeras brought Queen Azshara under his control in ages past. Using the cunning shaman as his conduit, the demon spread battle lust and savagery throughout the orc clans. Before long, the spiritual race was transformed into a bloodthirsty people. Kil'jaeden then urged Ner'zhul and his people to take the last step: to give themselves over entirely to the pursuit of death and war. Yet the old shaman, sensing that his people would be enslaved to hatred forever, somehow resisted the demon's command.
Frustrated by Ner'zhul's resistance, Kil'jaeden searched for another orc who would deliver his people into the Legion's hands. The clever demonlord finally found the willing disciple he sought - Ner'zhul's ambitious apprentice, Gul'dan. Kil'jaeden promised Gul'dan untold power in exchange for his utter obedience. The young orc became an avid student of demonic magic and developed into the most powerful mortal warlock in history. He taught other young orcs the arcane arts and strove to eradicate the orcs' shamanistic traditions. Gul'dan showed a new brand of magic to his brethren, a terrible new power that reeked of doom.
Kil'jaeden, seeking to tighten his hold over the orcs, helped Gul'dan found the Shadow Council, a secretive sect that manipulated the clans and spread the use of warlock magics throughout Draenor. As more and more orcs began to wield warlock magics, the gentle fields and streams of Draenor began to blacken and fade. Over time, the vast prairies the orcs had called home for generations withered away, leaving only red barren soil. The demon energies were slowly killing the world.
Rise of the Horde
The orcs became increasingly aggressive under the secret control of Gul'dan and his Shadow Council. They constructed massive arenas where the orcs honed their warrior skills in trials of combat and death. During this period, a few clan chieftains spoke out against the growing depravity in their race. One such chieftain, Durotan of the Frostwolf clan, warned against the orcs' losing themselves to hate and fury. His words fell on deaf ears, however, as stronger chieftains such as Grom Hellscream of the Warsong clan stepped forward to champion the new age of warfare and dominance.
Kil'jaeden knew that the orc clans were almost ready, but he needed to be certain of their ultimate loyalty. In secret, he had the Shadow Council summon Mannoroth the Destructor, the living vessel of destruction and rage. Gul'dan called the clan chieftains together and convinced them that drinking Mannoroth's raging blood would make them utterly invincible. Led by Grom Hellscream, all the clan chiefs except Durotan drank and thereby sealed their fates as slaves to the Burning Legion. Empowered by Mannoroth's rage, the chieftains unwittingly extended this subjugation to their unsuspecting brethren.
Consumed with the curse of this new bloodlust, the orcs sought to unleash their fury on any who stood before them. Sensing that the time had come, Gul'dan united the warring clans into a single unstoppable Horde. However, knowing that the various chieftains like Hellscream and Orgrim Doomhammer would vie for overall supremacy, Gul'dan set up a puppet warchief to rule over this new Horde. Blackhand the Destroyer, a particularly depraved and vicious orc warlord, was chosen to be Gul'dan's puppet. Under Blackhand's command, the Horde set out to test itself against the simple draenei.
Over the course of a few months, the Horde eradicated nearly every draenei living on Draenor. Only a scattered handful of survivors managed to evade the orcs' awesome wrath. Flushed with victory, Gul'dan reveled in the Horde's power and might. Still, he knew that without any enemies to fight, the Horde would consume itself with endless infighting in its unstoppable appetite for glorious slaughter.
Kil'jaeden knew that the Horde was finally prepared. The orcs had become the Burning Legion's greatest weapon. The cunning demon shared his knowledge with his waiting master, and Sargeras agreed that the time of his revenge had finally come.