@boag did you miss the part about not making something too powerful? Infinite energy generator once the people found out what it can do for them, they would definitely go to War over that.
@Wolvenworks Because most nobles from real history did act like that, Nobel's in that type of time period believed that they were better then everyone else and some times that included the Royal family'. Thus why many plots to kill kings have been founded by Nobles trying to get more power for themselves and their family.
Also why would there not be Monsters left over? Its been shown that the main fighting force most of the nations have are the people with powers and said powers get blocked by the Monsters. So most of the nations are not really set up to deal with them, and during the war if the Monster handlers died then the monsters went wild, hell in a recent chapter even with a handler they could go wild. So even if its just 10 of them out there they could do massive amounts of damage to Merchants and caravan guards, due to you needing really skilled people to actually fight them and even more so to kill them.