Simplify the following text for a Grade 9 native English-speaking person.
Original: The story is based on conflicts in the life of Carlos , Prince of Asturias ( 1545 â `` 1568 ) after his betrothed Elisabeth of Valois was married instead to his father Philip II of Spain as part of the peace treaty ending the Italian War of 1551-1559 between the Houses of Habsburg and Valois .
Simplified: Schillerâ s story is based on the true story of the life of Carlos , Prince of Asturias ( 1545-1568 ) who was promised that he could marry Elisabeth of Valois , but then his father , Philip II of Spain , changed his mind and married her himself . It was part of the peace treaty ending the Italian War of 1551-1559 between the Houses of Habsburg and Valois .