To expand on Sir Squirrel's post, at the beginning of each chapter is a chest for Advanced Scouts. You can not open the chest until you have finished enough provinces. Until you do, it will have a red number like 8/10 or 27/30 (where the first number will be red if you are below the minimum to open the chest). If you have scouted much more than that second number (i.e. 32/30, then you are pushing your scouts and paying more than you need to for the province, plus the enemies in the province will be very difficult to fight successfully. You will have to negotiate (which is all I do anyway) and it will cost more than it would if you scouted the province at the appropriate time.