helotism vs subjugation

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 

subjugation

noun
  • The state of being subjugated; forced control by others. 

  • The act of subjugating. 

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