Since the Iranians built their first kingdom in Balkh (Bactria, Daxia, Bukhdi) some scholars believe that it was from this area that different waves of Iranians spread to north-east Iran and Seistan region, where they, in part, became today's Persians, Tajiks, Pashtuns and Baluch people of the region. The changing climate has led to desertification since antiquity, when the region was very fertile. Its foundation is mythically ascribed to Keyumars, the first king of the world in Persian legend; and it is at least certain that, at a very early date, it was the rival of Ecbatana, Nineveh and Babylon.