You'd have my former soldiers invade your former realm that owes your present guild money due to the debt you previously incurred...
Simple
And now back to the topic at hand
Improve Unit is a court/free action. Since fighters have wage war as a bonus action, does that mean that, theoretically (if they can afford the active status) they can train their whole army each turn and drill them into an elite fighting force?
Thus veteran regulars can be turned into elite regulars in 4 turns (for 2GB - active status cost), for example, elite knights into crack in 5 (and the cost would be 10GB) etc..?