feudalism vs slavery

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. 

slavery

noun
  • An institution or social practice of owning human beings as property, especially for use as forced laborers. 

  • A condition of servitude endured by a slave. 

  • A condition in which one is captivated or subjugated, as by greed or drugs. 

  • Forced labor in general, regardless of legality. 

adj
  • Covered in slaver; slobbery. 

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