Note: This text is copied from the Warcraft II manual.
The Aftermath of the Second War
For long months the forces of the Alliance worked to seek out the renegade Orcs that had gone into hiding after the fall of the Dark Portal. The Blackrock, Dragonmaw, and Black Tooth Grin clans were captured by the Alliance and herded into guarded reserves and prison camps. While the leaders of the Alliance argued over what was to be done with them, Orgrim Doomhammer, the Warchief of the Horde, was placed under arrest and kept as an honored prisoner under the care of King Terenas of Lordaeron. Some members of the Alliance pleaded that the Orcs should be exterminated like animals, while others opted for a sentence of life imprisonment.
Having discussed the obvious benefits of a treaty with Doomhammer, King Terenas fervently hoped that the Orcs could be kept pacified long enough to eventually lose their lust for conquest. Thoras Trollbane of Stromgarde and Genn Greymane of Gilneas both disagreed vehemently with Terenas, resolving that the Orcs were too great a threat to leave alive. After months of debate and frustration, both leaders withdrew the support of their nations from the Alliance. Azeroth alone stood fast in its commitment to the Alliance. Even with the dynamic young Varian Wrynn seated upon Azeroth's throne, the distance between the kingdoms of Azeroth and Lordaeron made their union a hollow one.
Amid the strife that was slowly dissolving the great Alliance, the fact remained that the once vast numbers of the Horde were no more. The Twilight's Hammer and Stormreaver clans were decimated by their own brethren in civil wars that erupted during the War. The Burning Blade clan was routed and ultimately destroyed by troops under the command of Uther Lightbringer during the Final Battle at the Portal. Only the Bleeding Hollow clan was left unaccounted for as the cunning Kilrogg Deadeye managed to evade the best efforts of the Alliance to capture his clan. Elven scouts were placed on continual patrol within the Black Morass searching for any sign of the renegade Bleeding Hollow.
The Crossing of the Bleeding Hollow
Suspended ominously above the Black Morass, a tear in the fabric of reality hung like a disembodied eye, keeping watch over the ruins of the Dark Portal. This rift was the remnants of the twisted wizard Medivh's original Portal into Draenor - the dark, red world from which the Orcs passed into Azeroth. The Kirin Tor of Dalaran traveled to the land overlooking the ruins on this site and constructed the Citadel of Nethergarde to serve as guardian should the rift ever open again...
On the Eve of Summer in the year 606, a freak darkness swept across the Black Morass. All attempts by the mages at Nethergarde to probe into the darkness were futile, but they could sense that the rift was growing once more. Then, as if from a dream, the mages heard the sounds of a marching army. Hundreds strong, the sounds of armor and sword charged through the ruined portal and then as quickly fell silent. The thunderous shrieks of Dragons crying to the skies passed overhead, and then as suddenly disappeared into the gloom. Venomous undead whispers, barely audible under the clash of metal plates seemed to echo and repeat one phrase - "We will return..."
When the darkness lifted, the portal was visible once again. It illuminated the ruins as it always had, but the eerie light seemed to play tricks with the shadows. It was only upon closer inspection that the trampled mud that marked the passage of the Bleeding Hollow clan from Azeroth was found to be more than mere illusion.
The Old Clans
The Bleeding Hollow crossed over into Draenor and rejoined the 'old clans' that had never seen the fields of Azeroth. To many, the warriors of the Bleeding Hollow were considered mighty heroes as these Orcs had been living in the Human lands for over thirty years. Kilrogg met with the Elder Shaman Ner'zhul who now controlled the remaining clans in Draenor. The Shaman ordered that the newly arrived Death Knights, Trolls and Dragons were to be used by all of the clans in conjuncture. Ner'zhul also informed Kilrogg of his plan to retrieve certain artifacts from Azeroth as to open rifts into other worlds and take the Orcish Hordes to great victories beyond the Dark Portal...