Demographics
Khorasan was originally inhabited by the ancient Indo-Iranians in the Bactria–Margiana Archaeological Complex in around 2000 BC. The BMAC was a Bronze Age culture situated in the upper Amu Darya region of Khorasan. Airyanem Vaejah (Land of Aryans), which is mentioned in the Zoroastrian Avesta, is also believed by some scholars to be situated in the territories of Khorasan.
The Persian people appear to have been the first ethnic group to populate the region, but they began mixing with an increasing number of foreign invaders and as a result their proportionate number was reduced. Significant immigrants such as Arabs from the west since the 7th century and Turkic peoples after the Turkic migration from the north in the Middle Ages settled in the region. After Genghis Khan conquered Persia in the 13th century, great many of Mongols settled in Khorasan after depopulating its cities.
Read more about this topic: Greater Khorasan