improve vs pillage

improve

verb
  • To become better. 

  • To make (something) better; to increase the value or productivity (of something). 

pillage

verb
  • To loot or plunder by force, especially in time of war. 

noun
  • The act of pillaging. 

  • The spoils of war. 

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