The House of Kayus was established after an agreement between Iranian principalities and kingdoms and the Sasanian Empire, following a two-year war between the Empire and the local kingdoms. A local Iranian prince, Kayus, was reinstated tributary king to rule in northern Iraq.
Prior to the establishment of the House of Kayus, a number of unified Iranian principalities and kingdoms from Barzan and Hakkari to Mukriyan and Shahrazur ruled under the leadership of the Kingdom of Kerm (serpent) centered at Kermanshah. In AD 224, Ardashir I, founder of the Persian Sassanian Empire, challenged the kingdom of Kermanshah in a two-year war before finally receiving suzerainty from a number of kingdoms across the region. The House of Kayus was established in AD 226 and remained a semi-independent kingdom until AD 380 before Ardashir II removed the dynasty's last ruling member.
^ a: According to Mehrdad Izady they were Kurds, however, it is important to note that back then the word Kurd was a social term, designating Iranian nomads, rather than a concrete ethnic group.