he had the Shadow Council summon Mannoroth the Destructor

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. It was stressed that the majority of mankind could never know about the Guardians or the threat of the Legion for fear that they would riot in fear and paranoia. The elves agreed to the proposal and founded a secret society that would watch over the selection of the Guardian and help to stem the rise of chaos in the world.