@Kaarme
Related to africa's problem toward farmer not producing regular food : that's called cashcrops; the manga/ln "Genjitsushugi Yuusha no Oukoku Saikenki" goes in a bit about it near the start of the story.
@Akuma007e from trading with the merchants that comes to the territory three times per year, and as they only expend the bare minimum in their day-to-day life they save everything else.