Simplify the following text for a Grade 13 native English-speaking person.
Original: The first part consists of fifteen chapters , covering the Roman Catholic clericalism from the end of the nineteenth and beginning of the twentieth century in Austria-Hungary , then in the Kingdom of Yugoslavia .
Simplified: The first part consists of fifteen chapters , covering the Roman Catholic clericalism from the end of the nineteenth and beginning of the 20th century in Austria-Hungary , then in the Kingdom of Yugoslavia .