Why did the Franks manage to preserve and strengthen their kingdom?

The Franks waged wars of conquest, which in itself accelerated the process of state formation. They managed to achieve success due to the fact that there was a disintegration of the free community, which could be replaced by the arrival of an early feudal monarchy. There were no slaves in society, but there was a stratification: rich and poor appeared, for example, landowners and dependent peasants. One class subjugates the other.