Ethnopolitical governors the left and right wings (khanates) of the Turkic El (Empire).
The power after kagan belonged to “yabgu”, and he carried a military-administrative service. The title “Yabgu” was appropriated to sons of kagan or to his relatives in the paternal line. The title means “the assistant of the kagan”. Thus, after death of kagan yabgu should take the kagan’s place. During board of kagan there were two yabgus: töles yabγu > toles yabgu and tarduš yabγu > tardush yabgu. They ruled over two wings (parts) “töles and tarduš” which consisted of 300 thousand horsemen- soldiers. In each part the rank subordinated following way: šads (shads), apïts (apyts), tarhans and beks. Some researchers consider that “toles” is right wing, “tardush” is left wing; and “yabgu” is “the kagan of the right wing” (E.Shavann. A.N.Bernshtam). The dictionary of M.Kashgari says that “yafgu” is a title to give to a person not from kagan’s family, who occupies the position two steps lower that the kagan”.
Old Turkic word “yabγu//čabγu”. The root of the word is not clear. Nevertheless, if consider semantics of the Old Turkic root “yap-//jap -” means 1. “to do, carry out”, 2. “to come nearer, help”, “yabgu” was “the assistant of the kagan”.