helotism vs persecution

helotism

noun
  • The permanent oppression of a nominally free group of people 

  • A form of mutualism in which one species is forced to perform tasks for another, for their mutual benefit 

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 helotism and persecution occurred in a corpus of books? (source: Google Ngram Viewer )