This is an interesting question with a lot of right answers. In Europe specifically, the nobles of an area were originally warriors. They generally had horses and the money to equip a militia. So the early system became that the ones who could protect the land owned it and collected money from the people living there in return for that protection. Eventually nobles gained more and more power and armies rose to conquer other areas and larger "countries" emerged. The system of land inheritance and nobles giving each other higher and higher titles eventually led to kings and queens.