invasion vs occupation

invasion

noun
  • A military action consisting of armed forces of one geopolitical entity entering territory controlled by another such entity, generally with the objective of conquering territory or altering the established government. 

  • The breaching of the skin barrier. 

  • The spread of cancer cells, bacteries and such to the organism. 

  • The entry without consent of an individual or group into an area where they are not wanted. 

occupation

noun
  • The control of a country or region by a hostile military and/or paramilitary force. 

  • The act, process or state of possessing a place. 

  • An activity or task with which one occupies oneself; usually specifically the productive activity, service, trade, or craft for which one is regularly paid; a job. 

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