Germany makes sense because the Kaiser united several German Kingdoms, Russia did the same with its principalities.
But how did the colony of New Spain justify that it was the fanciest of sovereign states, an Empire?
Or is it as simple as nobody really cared about those kinds of things and you could have been the Emperor of New Zealand if you wanted.
you are thinking of Mexico as you know it today but back when the spaniards arrived in the new world there were several kingdoms in what is now Mexico (Tarascan, Tlaxcallan, Teotitlan, yoptzingo and mixtec) and that is only considered on the center of Mexico you also have to add the mayan to the south and the yaqui to the north the Spaniard in their conquest) if you go by the new spain borders you had the new kingdom of Leon, the kingdom of new Galicia the kingdom of Mexico, the kingdom of yucatan and the kingdom of Guatemala all in all they united several Kingdoms