[NOTE: From this reply by GRRM at "Not a Blog".]
The Dothraki were actually fashioned as an amalgam of a number of steppe and plains cultures... Mongols and Huns, certainly, but also Alans, Sioux, Cheyenne, and various other Amerindian tribes... seasoned with a dash of pure fantasy. So any resemblance to Arabs or Turks is coincidental. Well, except to the extent that the Turks were also originally horsemen of the steppes, not unlike the Alans, Huns, and the rest.
There do exist many other cultures and civilizations in my world, to be sure. The peoples of Yi Ti have been mentioned, as have the Jogos Nhai. I am not sure to what extent those peoples will ever enter this present story, however... their lands are very far away.
(I also have peoples and tribes that are pure fantasy constructs, like the Qartheen and the brindled men of Sothoryos).
In general, though, while I do draw inspiration from history, I try to avoid direct one-for-one transplants, whether of individuals or of entire cultures. Just as it not correct to say that Robert was Henry VIII or Edward IV, it would not be correct to say that the Dothraki are Mongols.