polity vs sovereign state

polity

noun
  • A politically organized unit; a state. 

  • An organizational structure of the government of a state, church, etc. 

sovereign state

noun
  • A state (country) which has sovereignty over a defined geographic area, is independent of any other country, and has its own government. 

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