Kings serve their people, and are served by them. Emperors have as many peoples as possible serving them. In a not-uncommon progression, Rome went from kings to a pseudo-Republic to a single Emperor.
The Republic periods are actually oligarchies run by wealthy aristocrats. As republics’ growth slows, the rich grow so rich the rest have little or nothing. Going to an emperor does not improve economic condition, but formalizes it.
The main difference between oligarchy and emperor is that an emperor allows favored groups of aristocrats to wipe out other groups of aristocrats.
Morally, emperors are no better than kings. Rome’s last king, Tarquin, was as much a womanizer as Caesar. Both were removed from office by aristocrats whom they hadn’t destroyed.
The Christians’ King rules those who consider that which is beyond creation, the Creator, or in Catholic Fundamentalist terms, from things that are programmed to Programmer.
When on earth, our King was not diverted by material things. Though His teachings seem absurd to the worldly, in whom else can His people believe?