Just an advise: try to "erase" from Your head the things You know about French, Germans, France, Germany, capital. Those are modern "images".
Easier said than done, especially when, the generation before Pepin, the Mayor had more power than the King, and often, more wealth. This is the time when people like Boniface persuaded the Pope to invest authority in the King, on condition that they undertook to spread the work of the Church of course, and also that title became heriditary. From this point, Kings ruled by the authority of God, via the Pope of course, a man who had the power to excommunicate the King and thereby remove his authority, In fact, Pepin the Short had been Mayor of the Palace but managed to depose the King, Childeric III, carefully coordinated with the nod from the Pope. This pivotal moment shaped european kingdoms and politics for the next 800 years