concordat vs federation

concordat

noun
  • A formal agreement between two parties, especially between a church and a state; specifically, an agreement between the Pope and a government. 

federation

noun
  • Act of joining together into a single political entity. 

  • Any society or organisation formed from separate groups or bodies. 

  • A collection of network or telecommunication providers that offer interoperability. 

  • Array of nations or states that are unified under one central authority which is elected by its members. 

adj
  • Of an architectural style popular around the time of federation. 

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