Why was the kingdom of the Franks more durable?

The kingdom of the Franks was a state machine. The whole life of the country was based on strict discipline and submission to the monarch. The Franks conquered the rich lands of the Western Roman Empire. Excellent Roman roads contributed to the growth of trade and complete control of the distant lands. By adopting Christianity, the Franks received spiritual and political advantages. With the blessing of the clergy, the army of the Franks seizes the lands of Gaul and along the Rhine River. Spirituality and faith raised the once barbarian tribes of the Franks to a higher standard of living.