[goldfinger]

Whoops I made a typo with the Ered Luin thing forgive me I ment Ered Mithrin.

I believe once Erebor was refounded, and Dain came with his people and those of Durin's folk still in the Ered Luin and elsewhere came to back to Erebor it became the most important of realms to Durin's folk for one their king resided there, and their was still gold jewels and others stuff inside the mountain. Still you're right, the Iron Hills were still very important to Durin's folk too and they did have a lot of traffic between them and Erebor.

You said that the Iron Hills kept out the Easterlings during the War of the Ring. Even though I would agree with you that they helped, I think we can only speculate that they did considering that Appendix B says:

"At the same time as the great armies besieged Minas Tirith a host of the allies of Sauron that had long threatened the borders of King Brand crossed the river Carnen, and Brand was driven back to Erebor. There they had the aid of the Dwarves of Erebor; and there was a great battle at the mountain's feet"

In the next paragraph it says:

"And the besieged came forth and routed them, and the remnant fled into the East and troubled Dale no more"

So that's why I say we can only speculate.

When I said end all be all I meant the appendices aren't the only thing that tells us important stuff about the Dwarves.

I find it strange though that there is the contradiction about the place that Durin's folk migrated to. A says North and B says South.

I have another question. Did the Firebeards and Broadbeams go back to the Ered Luin after the awakening of the Balrog, or did they go with the Longbeards?
I would think after thousands of years of these three houses living together, they would become intermingled and would no longer be separated by houses but would be of mixed blood lines and be just Durin's folk (those ruled by the line of Durin).
I've contemplated this question many times and haven't really come to a conclusion yet, so maybe some can give a good theory.