The statement that best analyzes the impact of Charlemagne’s changes on social structures within feudal monarchies is:
Nobles became an increasingly powerful social class due to land being divided among lords by monarchs.
This reflects the core aspect of feudalism where land ownership and the relationships between monarchs, nobles, and vassals defined the social hierarchy and power dynamics of the time. Charlemagne's policies reinforced the power of nobles through the granting of land, leading to the development of feudal structures where nobles held significant influence.