Dwarves of the Iron Hills
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The Dwarves of the Iron Hills belonged to the house of the Longbeards, otherwise known as Durin's folk. About half a millennium before the War of the Ring, the Dwarves of this house dwelt in the northern Grey Mountains, but they were greatly troubled by dragons in that region. After King Dáin I was slain by one of these dragons, his surviving sons led an exodus into the east. Dáin's elder son Thrór recreated the Kingdom under the Mountain at Erebor, while his younger brother Grór led a part of the people further into the east, to settle among the Iron Hills.
The Dwarves became strong and prosperous in their new home. And becoming the greatest realm of the North after the sacking of Erebor. They became well-known for making a metal mesh that could be used for making flexible items like leg-coverings. But more than anything these Dwarves became such a strong people that they were the only realm capable of stopping Sauron from attacking Rivendell and taking back the lands of Angmar.
These Dwarves of Durin's folk were known for being some of the most fierce and elite of all Dwarf armies. Their main weapon of choice seemed to have been the mattocks, though they also carried a short broad sword with a round shield.
Not much is said on whom were enemies of these dwarves, but it seems likely that the Easterlings were one of them, since their empire was near and around the Iron Hills, and possibly Dragons. Considering they lived in the wastes to the North.
War of the Dwarves and Orcs
During the War of the Dwarves and Orcs many Dwarves from the Iron Hills fought in the war, especially in the Battle of Azanulbizar in the year 2799. The Dwarves of the Iron Hills came to the battle in the most crucial moment, when the main Dwarf army was being decimated by the great host of Orcs. With these fresh reinforcments, the Dwarves were able to route and destroy the Orcs. Among those killed was their leader Azog, who was slain by (later king) Dáin Ironfoot out of vengeance for his father whom the great orc had killed earlier on in the battle.
After the coming of Smaug, most of the survivors of his attack went to the Iron Hills, except for Thrór and his small company of family and followers, who thought that they were the only survivors of the attack.
The two Dwarven peoples remained on friendly terms with one another. Years later, when Thrór's descendant Thorin Oakenshield sent to the Iron Hills for aid in restoring Erebor, Grór's grandson Dáin II Ironfoot (named after his illustrious ancestor Dáin I) sent many armoured Dwarves. As events developed, the Dwarves of the Iron Hills proved crucial in winning the ensuing Battle of Five Armies. Thorin died in that battle, and with him the royal line of Thrór. Through his ancestor Grór, the Kingship of Durin's Folk then fell on Dáin. As Dáin II Ironfoot, he removed from the Iron Hills, and re-established a kingdom under the Lonely Mountain.
It is possible, though not canonical, that the Dwarves from the Iron Hills, fought in the Battle of Dale against the Easterlings during the War of the Ring, but Tolkien never stated that they specifically did.