Northern Stronghold of the Orcs
Once a great realm of the Dwarves, Mount Gundabad became a capital of the orcs
in the northern climbs of the Misty Mountains.
Many have now forgotten, that once Mount Gundabad was a place fair and full of light. It was there in the heart of the Mountain, that Durin the Deathless first of the Dwarves was awoken. During the Years of the Trees in the first Age of Middle-earth, the Elves were awakened in the forests of Middle-earth and so began to awaken the trees. The Dwarves dug deep and found great treasure and ever after, Mount Gundabad became a place sacred to the line of Durin.
However, it would not always be so. In the Second Age of Middle-earth, Uruks under the power of Sauron invaded the Misty Mountains and plundered the riches of Mount Gundabad, taking it as their own. So began a bitter feud between the Orcs and Dwarves, who would never forget the taking of this most sacred of places. When Sauron fell in the Battle of the Last Alliance, the Orcs fled into the eastern wastes and the Dwarves reclaimed Gundabad and cleansed it of the rukhsaz filth.
In the Third Age of Middle-earth, when the Witch-king was sent North to Carn Dûm to assault Arnor, the orcs of the Misty Mountains gathered once more and took Mount Gundabad from the Dwarves. This time they held onto this strategic location, even after the fall of the Witch-king and made it the Orc Capital of the North.
It is said, the Uruks of the North built a great fortress with a mighty red tower, that was simply called Gundabad. It was constructed across the mountain pass that led to Mount Gundabad and then on to the frozen fortress of Carn Dûm. The tower and fortress of Gundabad, blocked the way to the mountain and so effectively sealed off Mount Gundabad from the Dwarves. Even after the Battle of the Five Armies, where so many of the Orcs of the Misty Mountains were slain, the Dwarves of Erebor still had not the numbers to retake either Mount Gundabad or Khazad-dûm.
Only after Sauron’s complete destruction, when the Ring went into the fires of Orodruin at the close of the Third Age of Middle-earth, were the dwarves able to consider retaking their lost Kingdom and the scared birthplace of Durin.
In the Battle of the Five Armies a great host of Orcs and Goblins came from Mount Gundabad in an attempt to win dominion of the North!
So began a battle that none had expected; and it was called the Battle of the Five Armies, and it was very terrible. Upon one side were the Goblins and Wild Wolves, and upon the other were Elves, Men and Dwarves. This is how it fell out.
Ever since the fall of the Great Goblin of the Misty Mountains the hatred of their race for the dwarves had been rekindled to fury. Messengers had passed to and fro between all their cities, colonies and strongholds, for they resolved now to win the dominion of the North.
Tidings they had gathered in secret ways; and in all the mountains there was a forging and an arming. Then they marched and gathered by hill and valley, going ever by tunnel or under dark, until around and beneath the great mountain of Gundabad of the North, where was their capital, a vast host was assembled ready to sweep down in time of storm unawares upon the South. Then they learned of the death of Smaug, and joy was in their hearts; and they hastened night after night though mountains, and came thus at last on sudden from the North hard on the heels of Dain. Not even the Ravens knew of their coming, until they came out in the broken lands which divided the Lonely Mountain from the hills behind.
From The Hobbit in the chapter ‘The Clouds Burst’