He couldn't create a standing army because he needed the nobility to raise and maintain it. The king had limited ability to tax because he had to have the approval of the nobles. The feudal system made it impossible for the king to centralize power. Then the lesser nobles would give land to serfs, and they would work it, providing labor in exchange for protection. The Nobles would then grant land to lesser nobles or knights in exchange for the vassals providing soldiers. They would create armies to protect him and the kingdom if he were attacked. In exchange, the nobles would pledge their loyalty to the king. The feudal system was an exchange of power that developed in the eighth and ninth centuries and lasted until the fifteenth.