encroachment vs invasion

encroachment

noun
  • An entry into a place or area that was previously uncommon; an advance beyond former borders; intrusion; incursion. 

  • That which is gained by such unlawful intrusion. 

  • An intrusion upon another's possessions or rights; infringement. 

  • An unlawful diminution of the possessions of another. 

invasion

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

  • 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. 

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