Why hadn't the dwarfs and elves, help fight at the Pelennor Fields, Black gate?

[auximenes]

IT'S DWARVES! NOT DWARFS!

I thought officially it was 'dwarfs', with a lower-case D.

[Bauglin]

I thought officially it was 'dwarfs', with a lower-case D.

It is (or was), but Tolkien used "dwarves" for reasons of his own (a quick blurb of which you can read here). Since then, however, "dwarves" has apparently become as accepted and as official as "dwarfs," at least as far as I can tell.

[Jewl_of_the_lake]

Time line from the Master himself from The Return of the king Appendix B
March 11 Eastern Rohan is invaded from the north. First assault on Lorien.
March 15 Battle under the trees of Mirkwood; Thranduil repels the forces of Dol Guldur. Second assault on Lorien.
March 17 Battle of Dale. King Brand and King Dain Ironfoot fall. Many Dwarves and Men take refuge in Erebor and are besieged.
March 22 Third assault on Lorien.

3 times Lorien had been assailed from Dol Guldur, but besides the valour of the elven people of that land, the power that dwelt there was too great for any to over come, unless Sauron had come there himself. Though grievous harm was done to the fair woods ont he borders, the assaults were driven back; and when the shadow passed, Celeborn came forth and led the host of Lorien over the Anduin in many boats. They took Dol Guldur, and Galadriel threw down its walls and laid bare its pits....

In the north also there had been war and evil. The realm of Thranduil was invaded, and there was long battle under the trees and great ruin of fire; but int he end Thranduil had the victory.

just a taste of the appendices found in the final book