 It may have been triggered due to the advent of hostile tribes on the eastern front of Iran.The war against the Hephthalites may have awakened the mythical rivalry existing between the Iranian Kayanian rulers and their Turanian enemies, which is demonstrated in the Younger Avesta.It may have thus been as a result of the conflict between Iran and its eastern enemies, that resulted in the adoption of the title of "kay", used by the very same Iranian mythical kings in their war against the Turanians in the East.