Like all dwarves, the Dark Iron dwarves of the Dark Iron clan are descendants of the earthen.(The below section originates from the book found in game: War of the Three Hammers while the rest of the content is source from Wowpedia and Warcraft Chronicles. I suggest to start reading the latter first and roll back for the vanilla lore for refreshment.)
The largest of the three clans, the Bronzebeards were led by the wilful Thane Madoran Bronzebeard. The clan, which formed the bulk of Ironforge's military and mercantile classes, considered itself the backbone of the kingdom and claimed to share distant blood relations with High Kind Modimus. The Bronzebeards themselves were tough, stubborn, and suspicious of their fellow dwarves, who they considered weaker.
Unlike the other two clans, the Wildhammer clan preferred to inhabit the craggy hills and icy slopes outside Ironforge, and were led by Khardros Wildhammer. They subsequently gained notoriety as adept and incredibly resilient mountaineers, for which they were proud. Thus considered uncouth by the Bronzebeards, the Wildhammers struggled to gain more sway with the High King and to solidify their place among the ruling elite of the city.
The Dark Irons, who inhabited the deepest and darkest corners of the subterranean city had a long-standing practice of dabbling in sorcery, along with a penchant for secrecy and political scheming, drew the ire of the majority of Ironforge's other inhabitants. Thane Thaurissan, however, held firm control over the kingdom's richest gem and mineral deposits, using this wealth as leverage to protect his people and secure a place in Ironforge's increasingly volatile political arena.
The Dark Iron clan was unsuccessful in wresting control of Ironforge from the Bronzebeard clan and Wildhammer clan during the Civil War and the historical clash within dwarfen society "War of the Three Hammers":
A member of none of the three clans, High King Modimus attempted to remain neutral in matters of government and always strove to treat each clan with fairness and respect. He was ineffective in attempting to reduce tension between the rival factions, however, and this would ultimately lead to catastrophe. Around 230 years before the first opening of the Dark Portal, High King Modimus Anvilmar passed away from old age. Before the rightful heir, Modimus' eldest son, could be crowned, the simmering cauldron of rivalry in Ironforge boiled over. Although no-one can be sure which clan struck first, the city soon fell into a state of open warfare. Each clan mobilized all of their resources and assets in an attempt to seize control of the mountain from the other two. Chaos reigned, and for years the war raged through the mighty halls and dark caverns of the once-thriving capital. Eventually, the Bronzebeard clan, using its martial expertise and large size, gained the upper hand and successfully defeated the Wildhammers and Dark Irons. The two beaten clans were driven from Ironforge, and the Bronzebeards claimed total control of the mountain and city.
Battered and weary from the war, Khardros Wildhammer and his clan gave up on Ironforge and left for the east. Soon, they settled in the nearby region of marshlands and highlands. There, they created a new city for themselves: Grim Batol. So magnificent and well-built was the city that it soon rivalled even Ironforge in its size and prestige. Although his clan's previous defeat weighed heavily on Khardros' heart, he and his kin came to accept their lot and became content and prospered in their new home. They lost interest in claiming Ironforge and neither made nor planned any attempts to wage hostilities against the Bronzebeards in their newly-claimed city.
Thaurissan and his Dark Irons vowed revenge against Ironforge. He took his followers south and founded a city within the beautiful Redridge Mountains. Despite years of prosperity, Thaurissan and his spell-weaving wife, Modgud did not soften in their desire to defeat the Bronzebeards and Wildhammers. After years of scheming, the Sorcerer-Thane was finally ready to act. In the recent lull since arriving in Redridge, he had begun building up large forces. Among the many Dark Iron warriors and battlemages, the clan's armies also included legions of the powerful and effective war golems, as well as devastating siege machines. With this new and diverse army, Thaurissan was confident that he could at least exact retribution on their dwarven cousins. The clan's plan of attack included a two-pronged invasion of both the Bronzebeard and Wildhammer territories simultaneously. The Sorcerer-Thane planned to lead one army to Ironforge himself and personally defeat the Bronzebeards, reclaiming the city. A second army led by his wife, the sorceress Modgud, would invade the Wildhammer's nation at the same time and seize their equally important capital of Grim Batol.
As planned, Thaurissan and his army marched deep into the Bronzebeard kingdom and eventually reached Ironforge. Using his vast siege engines and constructs, the Sorcerer-Thane struck deep into the city, forcing back the beleaguered Bronzebeard defenders. As in times past, battles raged across Ironforge's inner halls. Despite the Dark Iron's large forces, the Bronzebeard put up a stubborn and powerful defense. Only after Thaurissan had reached the very heart of the city itself was he halted. Having finally rallied his forces, Thane Madoran Bronzebeard began to push the Dark Iron clan from the city.
As events unfolded in Ironforge, Modgud had successfully lead her army to the Wildhammer capital and laid siege to it. The Wildhammers were surprised by this sudden assault but desperately held their ground against the invaders. Dark Iron mages and sorcerers used their dark magics to batter and break the Wildhammers' will. Led by Modgud, they brought the shadows of Grim Batol to life, transforming the bustling city into a realm of nightmare and shadow. The darkness itself began to stalk the dwarves in their own stronghold and soon began to take a major toll on the Wildhammers' strength. Desperate, Khardros Wildhammer led some of his best soldiers in a swift and brutal counterattack, which just succeeded in slaying Modgud herself. With her death, and a renewed Wildhammer resistance, the Dark Iron army fled south. Coordinating with the Wildhammer, Madoran learned of this recent development and brought his forces north. The Dark Irons were caught between the Bronzebeards and the Wildhammers; they were attacked from both sides and utterly annihilated.
As the Bronzebeard and Wildhammer armies closed in, Thaurissan desperately scrambled for a way to salvage the situation. He ultimately decided to draw on the fiery powers from deep within the world and use them as a powerful weapon. Thus, Thaurissan wove a great spell to save his kingdom. Yet, amid the conjuration, his mind turned to the death of his wife and his recent defeats. Anger roiled through Thaurissan's heart. His rage grew so absolute that his spellwork breached the Elemental Plane and tapped into a powerful being: Ragnaros, the Firelord. Unwittingly, Thaurissan ripped Ragnaros from the Elemental Plane and summoned him to the surface of Azeroth. The earth began to buckle and wrench apart, as the Firelord's violent arrival sparked a series of apocalyptic explosions that instantly killed the Sorcerer-Thane and shattered the surrounding mountains. From far away, Madoran and Khardros watched in horror as the world was torn asunder and firestorms engulfed the area. They realized in that instant that Thaurissan had doomed his people. Fearing for their own safety, the Wildhammers and Bronzebeards turned around and retreated back to their lands in the north. The war had, at last, reached its conclusion as his centuries old rule over his clan and the rocks remained untouched by outside hands until the first wave of the orc menace arrived...
Following the Sorcerer-Thane's quick and unintentional self-destructive passing in summoning Ragnaros the Fire Lord, the Wildhammer dwarves returned to their home of Grim Batol. But they found that Modgud's curse had left an evil taint in their fortress, and Grim Batol was uninhabitable. Ironforge offered them a home, but the Wildhammers refused, the majority of them turning north to settle in the Hinterlands, where they founded their new capital of Aerie Peak, while the rest settled in the region of Northeron, not far from their cursed former home.
One group of the dark iron's ranks since broke ties with their old brethren to seek out business relations with the Alliance and Horde as the two parties were set into conflict. This group is known as the Thorium Brotherhood.
