The War of Wrath destroyed much of Beleriand, and even lands far abroad saw great cataclysms. In the resulting havoc, devastation befell the holds of the Broadbeams and the Firebeards. Nogrod was utterly lost, its depths flooded by great subterranean waters, while much of Belegost collapsed, only the halls directly within its entry remaining intact. A great many Broadbeams and Firebeards perished as a result. The Broadbeams at that point were ruled by Dwálin II, named ‘the Wise’, son of Azaghâl of Belegost. The Firebeards were ruled by the young and impetuous King Thrur, nephew of King Naugladur, who had led the Firebeards of Nogrod in the disastrous sack of Menegroth before being slain by Beren Erchamion at the Battle of Sarn Athrad.

In the wake of the collapse of their ancestral homes, news spread to Khazad-dûm of the devastation of the halls of the western clans. While Durin the Deathless had passed recently, his son now ruled Khazad-dûm, and sent messengers to Dwálin II and Thrur, inviting their clans to come and settle in his own realm of Khazad-dûm, proclaiming “The Mountains have space and wealth enough for all my kin, and it is the duty of the eldest to look after the young. Come, and I shall help you delve new halls in splendor to equal those you have lost.”

Dwálin was not a king of temper or of pride and heeded the call of the King of the Longbeards, telling his people that to reclaim Belegost now would require more fortune and numbers than they could hope to afford – but that perhaps with the aid of the Longbeards, tied now in blood and kinship, they may once again reclaim it. Not all his people were willing to leave their ancient lands, however, nor to renounce their fealty to him for fealty to the Longbeard king. Under his second son a small remnant remained behind, delving new, much smaller holds in the mountains, awaiting the promised day when the elder line would return to reclaim their ancestral home. Thus the greater portion of the Broadbeams migrated to Khazad-dum, and became as one people.

Thrur of the Firebeards, however, was proud and young, and his people shared his fire. He felt the offer of Durin’s son was, if not meant as such, something of an insult to his people’s pride and ability. He acknowledged the wisdom of Dwálin – if Belegost could not be reclaimed without many years and great expense in treasure and lives, how much more for Nogrod to be born anew? In response instead, Thrur sought to make new halls all his own, away from his Broadbeam kin. Moving southwards, the Firebeards delved new halls in the southern Ered Luin, though these were shadows of the prosperity they once had known (for the mines of the southern Ered Luin, while rich in copper and iron, were poor in gold and jewels). Yet many of his people now questioned the wisdom of the royal line after the debacle of the Sack of Menegroth, and heeded the counsel of Dwálin, joining his people in their march to Khazad-dum, even one of Thrur's own brothers and a sister.

In total, roughly three-fourths of the Broadbeams and one-half of the Firebeards would migrate to Khazad-dum, though the records of Thrur instead protest merely one-third of his people left. The decision of so many of Thrur’s own people to ignore his own wishes to follow a Broadbeam and serve a Longbeard king (including two of his own siblings) would result in the Firebeards remaining somewhat cool and aloof from both clans, as well as their kin who joined them. Úri II would refuse to march with the Last Alliance, though he permitted his smiths to make weaponry for the Men of Arnor. It would only be in the early Third-Age that Úri III would meet with Cirdan of Lindon, Durin V, and the King of the Broadbeams, burying the hatchet and reconciling with them all.