enslavement vs peonage

enslavement

noun
  • The act of enslaving or the state of being a slave; bondage 

peonage

noun
  • The state of being a peon; the system of paying back debt through servitude and labour; loosely, any system of involuntary servitude. 

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