Review Detail of Lord_Fujin in Ruler of Iron and Flesh

The story is kind of childish, unthinkable things happen, for example: a slave of the defeated nation is turned into a soldier in the empire and within a few months can become part of the emperor's guard, he kills the emperor and his advisers and makes become emperor, and no one complains, at no time is it said how power is divided within the empire, is there no Nobles ?, as someone from an enemy nation who has been in the empire for a few months and has no political backing simply turns the emperor?