Prehistory
Kurdish is a language of the Northwestern Iranian group which has likely separated from the other dialects of Central Iran during the early centuries CE. Even though there are no records of the Kurdish language prior to the 13th century, the presence of Armenian loanwords indicates that there must have been Kurdish-Armenian contacts by at least 1100 CE.
The present state of knowledge about Kurdish allows, at least roughly, drawing the approximate borders of the areas where the main ethnic core of the speakers of the contemporary Kurdish dialects was formed. The most argued hypothesis on the localisation of the ethnic territory of the Kurds remains D.N. Mackenzie's theory, proposed in the early 1960s (Mackenzie 1961). Developing the ideas of P. Tedesco (1921: 255) and regarding the common phonetic isoglosses shared by Kurdish, Persian, and Baluchi, D.N. Mackenzie concluded that the speakers of these three languages form a unity within Northwestern Iranian. He has tried to reconstruct such a Persian-Kurdish-Baluchi linguistic unity presumably in the central parts of Iran. According to his theory, the Persians (or Proto-Persians) occupied the province of Fars in the southwest (proceeding from the assumption that the Achaemenids spoke Persian), the Baluchis (Proto-Baluchis) inhabited the central areas of Western Iran, and the Kurds (Proto-Kurds), in the wording of G. Windfuhr (1975: 459), lived either in northwestern Luristan or in the province of Isfahan.
Read more about this topic: History Of The Kurdish People