The Broadbeams were paired with the Firebeards, who lived in the Northern part of the Ered Luin when they were awakened by Eru Ilúvatar, before the First Age. They were prosperous in their great city of Belegost, trading with the Firebeards in the South, and also with the Sindar and Noldor of Beleriand, as well as the newly-appeared race of Men. The Broadbeams were a more friendly clan than the southern Firebeards, who were a more greedy and selfish house.
The Nauglamír, a jeweled necklace and one of the most beautiful treasures ever crafted in Arda, was made by the Broadbeams. The Broadbeams also helped build the city of Nargothrond for the Elves. Another famous item was the Dragon-helm of Dor-lómin, which was made by the famous dwarf-smith, Telchar.
In the Battle of Unnumbered Tears, the heavily-armoured Broadbeams, with their fearsome iron masks, held off the dragon Glaurung, as the sons of Fëanor retreated south to Ossiriand. During the battle, their great king, Azaghâl, was killed by Glaurung — but not before wounding the dragon with a dagger in the stomach. Glaurung screamed in pain and fled with many of the forces of Morgoth following him. Forgetting the battle, the Broadbeams then picked up their fallen leader and marched home.
The old kingdom of the Broadbeams came to a close in the War of Wrath with the breaking of the Ered Luin and the destruction of Beleriand, which sank beneath the waves. Belegost was ruined and the city of the Firebeards, Nogrod, was totally destroyed, sinking into the sea with much of the Ered Luin. Some of the Dwarves stayed to rebuild what they could of their kingdoms, but many left to go to Khazad-dum, home of the Longbeards.
In the Third Age it seems that the Broadbeams may have parted ways with Durin's folk along with the Firebeards, after the awakening of the Durin's Bane, and headed back to the Ered Luin, where things were probably much better than they were after the sinking of Beleriand. During this age also the Broadbeams more than likely answered the call of Durin's folk in there great mustering for the eventual War of the Dwarves and Orcs.