autocracy vs iron fist

autocracy

noun
  • An instance of this government. 

  • A form of government in which unlimited power is held by a single individual. 

iron fist

noun
  • Ruthless and usually unrestricted control. 

  • Symbol of an army's tank or cavalry branch. 

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