I have seen some of the previous questions asked about this on the subreddit, but haven't found any well-sourced answers.
(Making this as generic as possible, so that people feel comfortable submitting a range of answers:)
Say I am the headman of a pastoralist tribe, or coalition of tribes; we have entered a fertile river valley, besieged and captured the walled cities and fortifications, and driven out the previous owners. Now, I have heard that there is more profit to be had by taxing the surplus of this country, rather than picking up everything of value that I see and moving on to the next river valley.
Historically, what happened to the state apparatus following such a conquest? As an illiterate tribesman, how do I persuade the literate administrators that remain to collect taxes and deliver them to my tribesmen who remain?
Thanks!
The problem with making it generic is that they often tried different things.
For China at least, in general, they all quickly look to create a written script (if they didn't already) or look for help on that front. Some of the more successful administrators like the Jurchens (twice) were semi-nomadic, so they would have experience governing farming communities already have written script. Others, like the Mongols, tasked someone (often these semi-nomads) to make a written script for them. So I guess the first step for an illiterate tribesman to administrate a country is to become literate (and hire literate people).
The state and bureaucratic apparatus is pretty much kept in place aside from some minor changes, then with new branches set up to tackle administrating nomads. Some conquers (the Mongols is one) cut off the Han Chinese from all decision making processes though.
The Open Empire - Valerie Hansen
Search for Modern China - Jonathan Spence