A tributary empire exercises power by doing what?

A tributary empire has nominal governor in the tributary lands.

Explanation:

Tributary empires are those that are ruled by a nation that is not in direct control over all of its dominion and most of the states only pledge allegiance to it while retaining their own power structures.

This is something that happened often in the older times with the bigger empires that also had a sphere of influence in the regions they did not directly rule

Most of these regions only gave a part of the taxes to the main empire and sometimes supported the army.