expatriation vs immigration

expatriation

noun
  • voluntary migration from one's native land to another 

  • forced expulsion of from one's native land to another 

immigration

noun
  • The act of immigrating; the passing or coming into a country of which one is not native born for the purpose of permanent residence. 

  • The process of going through immigration checks at a border checkpoint. 

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