Simplify the following text for a Grade 9 native English-speaking person.
Original: Reversing the trend of the Umayyad period , when the Christian kingdoms of the north often had to pay tribute to the Caliph , the disintegration of the Caliphate left the rival Muslim kingdoms much weaker than their Christian counterparts , particularly the Castilian-Leonese monarchy , and had to submit to them , paying tributes known as parias .
Simplified: After the end of the Caliphate the rival Muslim kingdoms were much weaker than the Christian ones , and had to submit to them and to pay tribute .