Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. YAbgu was a state office in the early Turkic states, roughly equivalent to viceroy. THe title carried autonomy in different degrees, and its links with the central authority of Kagan varied from economical and political subordination to superficial political deference. THe position of Yabgu was traditionally given to the second highest member of a ruling clan (Ashina), with the first member being the Kagan himself. FRequently, Yabgu was a younger brother of the ruling Kagan, or a representative of the next generation, called Shad (blood prince). MAhmud Kashgari defined the title Yabgu as "position two steps below Kagan", listing heir apparent Shad a step above Yabgu. AS the centralized state disintegrated, the Yabgu was gaining more sovereignty, and historical records name a number of independent states with "Yabgu" being the title of the supreme ruler.