Back then kings had a lot of power, some kings use religion to their advantage as religion was seen as a big thing back then. They would seem to had a close relationship with god which made them have power over. authoriies
In addition to their religious authority, kings also had a great deal of political power. They were often the head of the government and had the final say in all matters of state. They also had control over the military and could do anything they want. Over time, as kingdoms grew larger and more complex, kings became even more powerful as they were able to centralize authority and control under their rule.
There are many other factors that can not be listed right here, but some main factors include, control over citizens and materials, the power to change laws, social, enconomics, religion, and social factors