[SauronOfMordor]

Races arise from people being in vastly different climatic conditions for many generations.

Middle Earth is about the size of Europe. Look up one of Tolkien’s maps. The Hobbits walked from one end to the other.

Maybe there were different races in other parts of that world, but they were not part of Tolkien’s story.

[IndispensableDestiny]

Maybe there were different races in other parts of that world, but they were not part of Tolkien’s story. The Haradrim (or Southrons) are part of LOTR. They are dark skinned.