feudalism vs subjugation

feudalism

noun
  • A social system based on personal ownership of resources and personal fealty between a suzerain (lord) and a vassal (subject). Defining characteristics are direct ownership of resources, personal loyalty, and a hierarchical social structure reinforced by religion. 

subjugation

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

  • The act of subjugating. 

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