mass murder vs persecution

mass murder

noun
  • The killing of a large number of people over a short period of time. 

persecution

noun
  • The act of persecuting. 

  • A program or campaign to subjugate or eliminate a specific group of people, often based on race, religion, sexuality, or social beliefs. 

How often have the words mass murder and persecution occurred in a corpus of books? (source: Google Ngram Viewer )