The dwarves are a whole different race, and it cooks itself apart, both because of their rare beginning as a race as well as the similitudes between them and elves & men and at the same time, how different they are from them.
Dwarves are persistent, reserved, laborious, that do not forget, stone and gem lovers (even more than life itself). But they are not evil by nature and few of them served the dark lord by their own will.
During the third age, there was a lot of zones with friendship among men and dwarves (dwarves knew and used the men's common tongue) but in secret and among them, they used their own tongue, and few other people other than dwarves know this tongue.
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