Kingdom of Dáin

Before Smaug sacked the Kingdom under the Mountain, its lord had been Thrór son of Dáin I, and Thrór escaped the Dragon's assault with his heirs Thráin and Thráin's son Thorin. Many decades later it was Thorin who recovered the Lonely Mountain after Smaug was slain. Almost immediately, the Battle of Five Armies was fought, in which Thorin was slain, along with his nephews Fíli and Kíli, leaving no direct heir to the Dwarf-kingdom.

The next in line to the throne was Dáin Ironfoot of the Iron Hills, a great-grandson of King Dáin I. Dáin Ironfoot, who had come to Thorin's aid and fought in the battle, was thus made King under the Mountain, becoming King Dáin II of Durin's Folk, and founding a prosperous realm known as the Kingdom of Dáin.

Many of the original companions of Thorin remained in Erebor with the new King, and his kingdom enjoyed peace for many years; Dáin himself was still its King at the time of the War of the Ring. In III 3019, when Dáin was two hundred and fifty-two years old, Sauron sent a great northern force against Erebor and neighbouring Dale, and the Battle of Dale was fought in the shadow of the Mountain. Despite his age, Dáin fought valiantly, but he was slain in the battle. Nonetheless, his kingdom survived: his son Thorin III was besieged for seven days within the Lonely Mountain, but when news of Sauron's defeat came north, the besiegers lost their will to fight, and the Dwarves and Men of Dale were able to break the siege and defeat their foes.