They might have been born into it, or rose into a position of leadership and didn't let go of it, or being wealthy and hiring people to kill anyone who didn't agree with you, making everyone follow you out of fear.
It could be a combination of these; someone born into wealth rose to the top by killing those who didn't agree, and never letting go of their position.
The monarch was able to maintain absolute control over the society with the addition of feudalism, which involved people being placed into different estates of power, such as: clergy, nobility and peasants. An absolute monarchy can best be seen in the words of Louis XIV in France when he proclaimed “I am the state”.
