I think this is more complicated than most people seem to recognize here. In the first place, race is not a biological category. This means that referring to race, even in a fictional story, will be based on social conventions of thinking (falsely or mistakenly) that people belong to distinct racial groups on the basis of, presumably, skin color. And it's hard to see how such views could arise, at least not without a very complicated back story. There could, of course, be geographically-isolated populations of humans or human-like creatures, and in these populations certain characteristics might be more common than in other geographically-isolated populations. But if that's the case, then these populations will not, except very rarely, interact, so it's not likely that there will be diverse populations; it won't be usual or normal. Second, most fantasies are imagined in some geographically-limited, temperate zone climate that is a close-clone of medieval Europe, and in that environment, with that technological level involving limited trade and travel, again, diverse populations (at least of the skin-color type) aren't at all likely. It's not that you can't have such things without stretching credulity (which is a weird concept to appeal to in a fantasy context), it's just that there aren't any clear reasons why 'different races' make sense. The "Summer Isles" in George Martin's Song of Ice and Fire series do provide a rationale, but even in that case, there aren't people of different races all over Westeros and Essos. In fantasies that have a clear line of descent from Tolkien's stories, diverse races don't make sense at all (even supposing isolated developments in the 'east' of Middle Earth) because the time frames involved are only thousands of years, not millions. Again, it's not that such things cannot be introduced, but the matter is, as i said, complicated.