Black Empire

The Black Empire was the dark civilization established by the Old Gods after their arrival on primordial Azeroth. It reigned over much of the world after the Elemental Lords and their armies failed to repel the Old Gods. The empire was ultimately destroyed by the titan-forged armies of the Pantheon.

After the Fourth War, the Black Empire was recreated by N'Zoth, before being defeated by Azeroth's champions with the Heart of Azeroth.

Ancient times
After slamming into Azeroth from the Great Dark Beyond, the Old Gods embedded themselves in the world's surface and sent their tentacles slithering towards the planet's defenseless core and its nascent world-soul. As they spread their corruptive influence across the land, two races arose from the organic matter that seeped from their blighted forms: the cunning n'raqi and the resilient aqir. The n'raqi, or "faceless ones", acted as taskmasters, employing the insectoid aqir to build massive citadels and temples around the massive bulks of their Old God masters. The greatest of these bastions was built around Y'Shaarj, the most powerful and wicked of the Old Gods. This burgeoning civilization was located near the center of Azeroth's largest continent, and soon the holdings of Y'Shaarj and the other Old Gods would spread across the world, becoming known as the Black Empire. Massive sacrifices and living buildings filled with void energy were some of the distinguishing features of this shadowy domain.

The rise of the Black Empire did not go unnoticed by the Elemental Lords, who had previously been the only inhabitants of Azeroth. Seeing the Old Ones as a threat to their dominion, for the first time in Azeroth's history, the native spirits of the world united against a common enemy. Ultimately, however, the elementals could not stand against the endless swarms of n'raqi and aqir, and the Old Gods eventually succeeded in enslaving the Elemental Lords. Without the native spirits of the world to hinder the Old Gods' influence, the Black Empire's borders crept over much of the desiccated world. Perpetual twilight descended upon Azeroth, and the world spiraled into an abyss of death and suffering.

The Old Gods constantly fought against each other, through infinite armies that clashed in ceaseless battle. The forces of N'Zoth, led by the C'Thraxxi Warlord Zon'ozz, waged endless war against the forces of C'Thun and Yogg-Saron and at one point, N'Zoth also lost a great battle to Y'Shaarj in the land now known as the Broken Shore. However, as was so often the case, even defeat ultimately worked in N'Zoth's favor.

Arrival of the titans
One day, however, the titans arrived with the intention of purging Azeroth of the Old Gods' corruption and saving its growing world-soul. As the titans' bodies were too massive for them to take action directly without risking permanent harm to the planet, they instead crafted the mighty titan-forged — the aesir and the vanir — to do battle in their stead. The titan-forged succeeded in defeating the Elemental Lords and sealing them in an Elemental Plane and destroyed most of the aqiri race, but when they began making their way towards the temple city of Y'Shaarj, the Pantheon feared that the Old God would prove too great a challenge for them. Aman'Thul the Highfather decided to take direct action, despite the risk of inflicting permanent damage to the planet. Thus, he reached down through Azeroth's skies and ripped Y'Shaarj from the surface of the world, tearing the Old God apart and obliterating hundreds of titan-forged in the process. To the titans' horror, a great wound was left in Y'Shaarj's wake, and the world-soul's arcane lifeblood erupted from the scar to roil out across the world. The Pantheon realized that the Old Gods had burrowed far deeper into the surface than anticipated, and they could not risk excising the remaining three Old Ones, lest Azeroth be completely destroyed. Instead, the Pantheon ordered their titan-forged servants to imprison the remaining Old Gods and contain their evil below the earth, rather than outright killing them.

After several long and difficult battles, the titan-forged succeeded in imprisoning N'Zoth, C'Thun and Yogg-Saron where they lay, even after Yogg-Saron unleashed its mighty C'Thraxxi generals. The Black Empire was no more, and for the first time in Azeroth's history, a tentative peace settled over the world.

Modern times
Even after the Black Empire's fall, the Old Gods continue to influence the mortal world through whomever they can influence and enslave, and they have repeatedly sought to reassert their dominion over Azeroth by recreating the Black Empire, such as during the First War.

Cataclysm
After arriving on Azeroth, Cho'gall and the Twilight's Hammer clan heard the whispers of the Old Gods, who showed the orcs and ogre visions of the terrible glory of the Black Empire, which the Twilight's Hammer could help rebuild as a way of heralding the Hour of Twilight. During the Cataclysm, N'Zoth intended to use Deathwing to restore the Black Empire and shroud the world in shadow.

At least some powerful n'raqi also seek to reforge the Black Empire and restore it to its former glory.

Battle for Azeroth
The blood trolls of Nazmir serving G'huun aimed to free the Old God in order to restore the Black Empire.

Later during Investigating the Halls, Wrathion surmises that the nightmarish visions seen by the player is a future with a restored Black Empire, and theorizes that this is N'Zoth's ultimate goal. Wrathion later surmises that N'Zoth intends to do so by seizing control of the Forge of Origination and use the Reorigination Protocol to transform Azeroth. At N'Zoth's command, the Black Empire assaults the Vale of Eternal Blossoms and Uldum under the command of Vil'raxx and Black Warden Rhothkozz, respectively.

Seeking to stop N'Zoth from claiming Azeroth, champions of the Horde and Alliance invaded Ny'alotha, the Waking City combating the Black Empire and ultimately defeating, and presumably killing, N'Zoth.

Notes and trivia

 * The term "Black Empire" as a name for the Old Gods' ancient empire was first used by Chris Metzen during the Mists of Pandaria launch live stream in 2012. The name would not be officially mentioned again until 2015, when all of the artifact weapons and their backstories from World of Warcraft: Legion were revealed on the official site, and the concept was further expanded upon in World of Warcraft: Chronicle Volume 1 in 2016.
 * The terrifying dagger known as Xal'atath, Blade of the Black Empire was made from the claw of an Old God eons ago, and dark priests used it for ritual sacrifices during the height of the Black Empire. It is said that the blade can grant its owner visions of the Black Empire, but all who have looked upon such horrors have lost themselves to madness.
 * The titan watcher Highkeeper Ra wielded the Fist of Ra-den in battle against the Black Empire for years beyond counting.
 * The Temple of Elune in Suramar was unknowingly built where a mighty structure of the Black Empire once stood.
 * The titan-forged refer to it as the era of "Shadow".
 * One of Toki's farewell quotes is "Never accept gifts from the Black Empire".

Speculation



 * Xal'atath makes several remarks regarding the Broken Shore and its connection to the Old Gods. The dagger claims that the Tomb of Sargeras pales in comparison to the grandeur of what stood there long ago. It explains that Thal'dranath was always a place of power, and that Aegwynn was drawn there, as were the elves, the trolls, and something else, likely the Old Gods. Furthermore, Xal'atath claims that the land had not seen "such carnage" since the Battle for K'tanth, which occurred "long ago", and that it was "here" in ages past that the God of the Deep lost a great battle to the God of Seven Heads, though the defeat ultimately worked in N'Zoth's favor. Thus, it can be speculated that the battle between N'Zoth and Y'Shaarj was fought over this place of power and the great edifice that stood there long ago, possibly named K'tanth, or alternatively what was situated beneath it.
 * The edifice might have been destroyed during this battle, by the elemental armies that brought down the temples of the Old Gods, or by the titan-forged who destroyed the Black Empire.
 * Xal'atath mentions an event called "the Scouring" in its quote whisper This likely refers to the fall of the Black Empire and the subsequent scouring of the aqir and n'raqi by the titan-forged forces.
 * Based on Mindflayer Kaahrj's speech, the Black Empire appears to be called "Shath'mag" in the Shath'Yar language.