There were refugees everywhere during the Three Kingdoms. The ones that fled to Wu ended up serving in the military or on the lands of a rich or noble family. Some fled with Liu Bei (for some reason) and either ended up in the military or became merchants in Shu Han or served on the lands of rich nobles.
Those that stayed up north were given lands by Cao Cao in exchange for military service. As the war up north had destroyed so much of the area and left so much deserted land Cao Cao organized it into agro-military colonies. Basically Cao Cao cut out the nobility and confiscated lands that were not being used creating settlements where soldiers and their families could live. The soldiers trained and guarded the territory while their families farmed, their children could then serve as soldiers as well (or some other form of tax). This provided a constant stream of soldiers which had the required training to be put into service (I mean land, food and employment is a pretty good deal). This system stopped when Jin usurped Wei and instead they began partitioning the land amongst the nobility and the rich landed elite. The Ming also tried this early on but ended the system for reason that are unclear to me.
If you want to do a story you might try the Ming dynasty. Jinyiwei could be an interesting protagonist being in charge of arrests, torture, some fighting and guarding as well. Would make for an interesting and well rounded character.
Now every time I think of Ming I get this (Warning: really violent) https://www.youtube.com/watch?v=WiS0ABHCkao