regency vs sovereign polity

regency

noun
  • The time during which a regent is in power. 

  • An administrative division ranking below a province in Indonesia. 

  • A system of government that substitutes for the reign of a king or queen when that king or queen becomes unable to rule. 

sovereign polity

noun
  • any sovereign polity 

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