feudalism vs mastery

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. 

mastery

noun
  • Superiority in war or competition; victory; triumph; preeminence. 

  • The position or authority of a master; dominion; command; supremacy; superiority. 

  • The act or process of mastering; the state of having mastered; expertise. 

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